Remove generated HTML documentation from version control

As it is generated by the build system it doesn't have to be checked
in, and having it in became a whole lot more annoying since it started
being generated automatically on `make all` instead of specific (and
weird) `make doc`, as it means whenever the documentation changes the
HTML is re-generated on any make run.  This is particularly problematic
if using a different Docutils version than the one used to generate the
checked-in version as it would create local noise that should not be
committed, yet keep being annoying.

This situation probably leads to most people disabling (or at least,
not enabling) the documentation generation on normal builds, itself
leading to more hassle updating of the documentation.

.gitignore

@@ -99,6 +99,7 @@ Makefile.in
 /doc/Doxyfile
 /doc/Doxyfile.stamp
 /doc/geany.1
+/doc/geany.html
 /doc/hacking.html
 /doc/*.pdf
 /doc/*.aux