all: implement macro "footnote:"

Macro footnote grammar,

----
"footnote:" [ REF_ID ] "[" STRING "]"
----

In asciidoctor, footnote can be placed anywhere, even after WORD without
space in between.

The REF_ID, define the unique ID for footnote and can be used to reference
the previous footnote.
The first footnote with REF_ID, should have the STRING defined.
The next footnote with the same REF_ID, should not have the STRING
defined; if its defined, the STRING is ignored.

1 files changed, 56 insertions, 0 deletions

diff --git a/testdata/inline_parser/macro_footnote_externalized_test.txt b/testdata/inline_parser/macro_footnote_externalized_test.txt
new file mode 100644
index 0000000..bd8736c
--- /dev/null
+++ b/testdata/inline_parser/macro_footnote_externalized_test.txt
@@ -0,0 +1,56 @@
+>>> input.adoc
+:fn-hail-and-rainbow: footnote:[The _double_ hail-and-rainbow level makes my toes tingle.]
+:fn-disclaimer: footnote:disclaimer[Opinions are my own.]
+
+The hail-and-rainbow protocol can be initiated at five levels:
+
+. double{fn-hail-and-rainbow}
+. tertiary
+. supernumerary
+. supermassive
+. apocalyptic
+
+A bold statement!{fn-disclaimer}
+
+Another outrageous statement.{fn-disclaimer}
+
+<<< output.html
+
+<div class="paragraph">
+<p>The hail-and-rainbow protocol can be initiated at five levels:</p>
+</div>
+<div class="olist arabic">
+<ol class="arabic">
+<li>
+<p>double<sup class="footnote">[<a id="_footnoteref_1" class="footnote" href="#_footnotedef_1" title="View footnote.">1</a>]</sup>
+</p>
+</li>
+<li>
+<p>tertiary</p>
+</li>
+<li>
+<p>supernumerary</p>
+</li>
+<li>
+<p>supermassive</p>
+</li>
+<li>
+<p>apocalyptic</p>
+</li>
+</ol>
+</div>
+<div class="paragraph">
+<p>A bold statement!<sup class="footnote" id="_footnote_disclaimer">[<a id="_footnoteref_2" class="footnote" href="#_footnotedef_2" title="View footnote.">2</a>]</sup></p>
+</div>
+<div class="paragraph">
+<p>Another outrageous statement.<sup class="footnoteref">[<a class="footnote" href="#_footnotedef_2" title="View footnote.">2</a>]</sup></p>
+</div>
+<div id="footnotes">
+<hr>
+<div class="footnote" id="_footnotedef_1">
+<a href="#_footnoteref_1">1</a>. The <em>double</em> hail-and-rainbow level makes my toes tingle.
+</div>
+<div class="footnote" id="_footnotedef_2">
+<a href="#_footnoteref_2">2</a>. Opinions are my own.
+</div>
+</div>