utils: Allow links to have custom text

Use the idiomatic Markdown form:

    [text][link]

format, where "link" is our homegrown link syntax, and text is a subset
of word characters, spaces, and punctuation marks.

Fixes: #100
3 jobs for link-text in 1 minute and 38 seconds (queued for 5 seconds)
Status Name Job ID Coverage
  Check
passed flake8 #1467554

00:01:38

failed mypy #1467555
allowed to fail

00:01:33

passed reuse #1467556

00:01:38

 
Name Stage Failure
failed
mypy Check
gidocgen/gir/parser.py:982: error: Argument "get_type" to "GType" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:1004: error: Argument "name" to "Union" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:1004: error: Argument "symbol_prefix" to "Union" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:1004: error: Argument "ctype" to "Union" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:1006: error: Argument 1 to "set_version" of "GIRElement" has incompatible type "Optional[str]"; expected "str"
gidocgen/utils.py:814: error: Need type annotation for 'found_programs' (hint: "found_programs: Dict[<type>, <type>] = ...")
Found 205 errors in 3 files (checked 17 source files)
Cleaning up file based variables
ERROR: Job failed: exit code 1