Closes #3432760.

Not every filetype for a specific lexer implements type keywords even if the
lexer supports it.

This prevents GTK of trying to fetch the necessary information like
MIME-type itself, which leads to a significant speedup (> 30%), as
well as using the real MIME-type we use rather than the GIO-guessed
one.

Use foreach_document() in a few places where appropriate and make
some code more consistent.

These add noise to the code with little real benefit.

This function was only used from document_create() and most of this code is
not needed since the memset() and g_new0() calls set the memory to all 0's,
which in this case should suffice to (re)set all the members to 0/NULL/FALSE.

Refactor so all the resetting to defaults code is done in remove_page()
only and then only do the required non-FALSE/NULL initialization in
document_create().

Move the remove_page() prototype to the top of the file and various other
minor changes in remove_page().

It was used only in one place in document_update_type_keywords() which
already did a similar check using the file type before calling this function.

Update HACKING file and very minor cleanup of other code in
document_update_type_keywords().

Previously an error message was shown if doc->file_name is NULL.

The Save As dialog is now shown if the document does not have an
absolute path. This is because the user should confirm where to save
the document in this case.

Although this changes plugin API behaviour, it seems the best way to
ensure the Save As dialog is always shown when needed so the user
knows where the document has been saved.

Also fixes a doxygen warning.

Fix correctly checking result of editor_lexer_get_type_keyword_idx().
Do not check IS_SCINTILLA unnecessarily (this is covered by DOC_VALID).
Do not use G_[UN]LIKELY macros as this complicates code without any
real benefit (unless in a tight loop).

Unix path separators can occur e.g. when using MSYS.
Windows does not allow filenames to contain Unix path separators so
this should be safe.

Finding paths in the tree was not case-insensitive either.

Use case-insensitive matching for project base path and home
directory in document filenames.

This is useful if one have many open files from different directories
and wants to see the files from only one or another.

This makes the code more readable, potentially more future-proof (if
the actual string changes) and better style (catches possible typos at
build-time).

Use two spaces instead of tabs, spaces between function and opening
argument bracket, and various minor changes.

Add dummy gpointer to private struct so the class can be compiled
without modification.

On most systems Geany is running inside an GTK/GNOME environment.
As a matter of this fact we can assume evince is the default PDF-viewer.

This way, Geany's standard out and error can be read if started in verbose
mode until a key is pressed which makes debugging of command line
actions easier.

This enables us to wait for input in the debug console window
and so keep it open if necessary until there is some input of
the user.

Fixes bug #3425969.  Replace Geany escaping of session filepaths
with g_uri_escape_string (available now in 2.16) allowing any
punctuation characters in the path.

Adds the ability to set filetype on open by extracting it from the
file using a regex on the first few lines (default 2).