Release share v0.30.0 (2021-10-04)

=== Breaking changes

*  lib/io: separate FileState for updated mode and content

   Previously, when content of file being watched is modified, it will
   trigger the callback with State set to FileStateModified.  When the
   mode of file is modified, it will also trigger the callback with
   the same state.

   This changes separated those state into two kind: FileStateUpdateMode
   for update on file mode, and FileStateUpdateContent for update on
   file content.

=== New features

*  lib/memfs: export the Node Update method

   The Update method update the node metadata or content based on new
   file information.
   It accept two parameters: the new file information, newInfo, and
   maximum file size, maxFileSize.

   The newInfo parameter is optional, if its nil, it will read the file
   information based on node's SysPath.

   The maxFileSize parameter is also optional.
   If its negative, the node content will not be updated.
   If its zero, it will default to 5 MB.

   There are two possible changes that will happen: its either change on
   mode or change on content (size and modtime).
   Change on mode will not affect the content of node.

*  lib/strings: add function Alnum

   The Alnum remove non alpha-numeric character from text and return it.
   Its accept the string to be cleanup and boolean parameter withSpace.
   If withSpace is true then white space is allowed, otherwise it would
   also be removed from text.

=== Bug fixes

*  lib/memfs: fix symlink to directory not included on mount

   During mounting and scanning a directory, if the node is symlink to a
   directory, the isIncluded will return false because the node is not
   a file nor directory.

   The fix is to check if node mode is symlink first and then get the
   the real stat.

*  lib/io: fix NewWatcher when called DirWatcher

   When NewWatcher called from DirWatcher's Start(), it will called NewNode
   with nil parent parameter.  If the parent parameter is nil on NewNode
   the SysPath of new node will be set to the FileInfo.Name() instead of
   full or relative path based on current working directory.

   Any operation using new node SysPath will failed because the path
   does not exist or reachable from current directory.

   For example, let say we have the following directory tree,

     testdata
      |
      +--- A
      |
      +--- B

   We then set DirWatcher Root to "testdata" from current directory.
   The DirWatcher Start then iterate over all child of "testdata" directory,
   and call NewWatcher("testdata/A", ...). On the NewWatcher, it will
   call NewNode(nil, FileInfo, -1).  Now since the parent is nil,
   the Node.SysPath will be set to FileInfo.Name() or base name of the file,
   which is "A".

   Later, when node content need to be read, ioutil.ReadFile("A") will
   fail because the path to "A" does not exist on current directory.

   This fix require to force the parameter "parent" on NewNode to be
   required.

*  lib/memfs: fix possible data race on PathNode

   During Memfs Get(), if the node returned by PathNodes.Get() is null,
   the memfs instance will try to refresh the directory tree. In case
   the requested path exist, the memfs will write to PathNodes through
   AddChild()

   At the same time, there maybe a request to access another path, which
   cause both read and write occured.

*  lib/memfs: fix NewNode if node is symlink to directory

   Previously, if a symlink point to directory the memfs NewNode function
   will return an error,

     AddChild wui: NewNode: read x/y: is a directory

   which cause the files inside y cannot be scanned (404).

   This commit fix this issue by checking if the original node mode is a
   directory and return immediately.

=== Enhancements

*  lib/memfs: check error on File Close on GoGenerate

   Previously, we ignore the error for call to Close when there is an
   error in previous operation.

   This changes check the error returned from Close and add it to the
   returned error message.

   While at it, use consisten prefix for all returned error:
   "MemFS.GoGenerate".

*  lib/http: support server caching file system using ETag

   If the Server handle file system using MemFS, server will set the
   ETag [1] header using the file epoch as value.

   On the next request, server will compare the request header
   If-None-Match with the requested file epoch. If its equal server will
   return the response as 304 StatusNotModified.

   [1] https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag

*  lib/xmlrpc: convert the value using Sprintf on GetFieldAsString

   Previously, the GetFieldAsString will return empty string if the
   Value type is not string.

   In this commit, we force the value to be string by converted it using
   fmt.Sprintf.

*  math/big: add some examples of Rat.Int64() and RoundToNearestAway

=== Chores

*  github: update the Go version to v1.17.1

*  lib/strings: update comment and example of TrimAlnum
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