Protect private definitions by the GEANY_PRIVATE macro in headers

Only manually uninstall the files we manually installed, as
uninstall-local might be run in parallel to Automake's own uninstall
targets.

We don't uninstall the directories as some docs seems to suggest
`rmdir` isn't really portable.  Anyway, Automake don't uninstall
directories either so it's not a real problem.

An alternative solution would be to keep the recursive removal of
`$(DOCDIR)` but move it to `uninstall-hook`, which is guaranteed to be
run after other uninstall rules.  However, recursive deletion is not
always sensible as it might remove files we didn't install, e.g. if the
user added them manually.

We don't distribute it, so we need to clean it.

So they become part of tarball.

Make documents_array public and accessible by doxygen and describe all
parameters of tm_source_file_new().

On startup, the Geany main window doesn't have a GdkWindow yet
(probably because it is not yet mapped). This causes many
'gdkdrawable-win32.c:2013 drawable is not a pixmap or window'
warnings when resolving shortcuts on Windows.
Since we pass the SLR_NO_UI to the Windows API, we probably
don't need the parent hWnd reference at all.

Don't rebuild TagManager workspace tags when quitting

Don't prompt for reload from infobar when there are no unsaved changes

Changed wrong translation of identation

When editor_create_widget() is used on an editor with already existing
widget, don't reset the internal indentation settings of that editor.

Closes #189

Updating the workspace is useless as the application will be shut down,
and not doing it can save a lot of time (almost 50% speedup quitting an
instance with all Geany source from `src/` open).

Also warn about losing undo history when there are no changes.

In addition, this patch defines the GEANY_PRIVATE macro for the tag
manager library where it wasn't defined before, removes 2 tag manager
headers from distribution as they are not needed by plugins and
in the tag manager changes the docstrings to ordinary comments for
private definitions.

3e089e4c accidentally switched from
`g_get_user_config_dir()` to `g_get_user_data_dir()` as the location
for the user's configuration directory.

Force disk check before save to prevent accidental overwriting

Add project prefs for line breaking column & multiline comment completion

Remove unused tag manager files

Before we used g_get_user_config_dir() but GLib changed the returned
location in newer versions, so use the Windows API directly
to get the old location, at least for now.
Also add utils_get_user_config_dir() wrapper.

Code is based almost completely on a patch from Matthew.