API documentation index had spaces between link caption and URL,
which may be unsupported by some Markdown implementations.
That is, "[caption](URL)" is valid but "[caption] (URL)" is not.
The problematic behavior is observed with Doxygen on Windows.
Remove the spaces.
Unfortunately, Markdown syntax is not formally specified.
Fixes: 9bf486e606b0 ("doc: generate HTML for API with doxygen") Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>