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.

Fix typo in README

Useful e.g. with Save All when the modified file is not the current tab.

Don't use `g_regex_get_compile_flags()` that is new in 2.26, but we
only depend on 2.20.

Closes #340.

Project line wrapping pref

Fix adding stash group and applying defaults.
Don't let Properties dialog override per-document line wrapping state.
Use "editor" for key group name.
Remove code already handled by stash group.

Notify user when trying to save read-only document

Confirm infobar reload when document has modifications

New name is clearer against document_reload_prompt.
Add deprecated alias.

Don't set document text as changed when file on disk is newer

Setting the document text as changed makes it too easy to accidentally
overwrite the file - e.g. when closing you're reminded to save it.
It also makes it slower to close documents you no longer want open.
Setting text as changed is still done if the user cancels the warning.

Confirm whether to save protected documents instead of ignoring save

(Reuses existing strings).