Release share v0.49.0 (2023-08-04)

In this release we refactoring lib/ssh, ssh/config; bug fixes in
lib/http.HandleFS, lib/os.Extract, lib/smtp.NewMailTx; new functions
Environments, PathFold, and PathUnfold in lib/os,
LoadPrivateKeyInteractive in lib/ssh.

In lib/ssh, we rename NewClientFromConfig into NewClientInteractive and
make only the valid SSH key added to the agent automatically once
connected, not all of SSH keys from IdentityFile.

In ssh/config, we simplify the struct Config by using a Field, a map of
key and value, instead of multiple fields with different types.
As a helper, we provide method FieldBool, FieldInt, Hostname, User, and
Port.

The fix in http.HandleFS related to missing request query when the
requested resource is directory.

The fix in os.Extract related to Zip Slip vulnerability.
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