We cannot compute the length in characters after the text has been
deleted, so we need to compute it in BEFOREDELETE.  However, we need to
emit the signal once the buffer has actually changed, so we need to
cache the value in-between those events.

This doesn't support nested templates or escaped `es, but at least
handles the most obvious cases for now.

Part of #934.

Closes #1339

It actually introduces a few new things worth mentioning.

Say hello to Geany 1.30 "Calron"!

Windows: Improve executing external commands on non-ASCII paths,
effectively fixing most known issues.

Use pre-compiled 'grep' binary from MSYS2 on Windows

This restores the previous behavior as it has been on non-Windows
systems before.
Post-1.29 we will merge #1300 which implements run helper script support
for non-Windows systems more sophisticated.

utils_get_utf8_from_locale() is actually a no-op on Windows, so use the
GLib conversion directly.  We really mean locale here, not "filename
encoding".

Apparently using arguments instead of putting paths directly in the
script is enough for it to work on Windows, so use a simple script
instead of a program, so it's both shorter and easier to tune.

This removes all encoding issues from passing on a script to cmd.exe on
Windows, as it now uses proper wide character API there.

Not much changes on other OSes, but we don't create temporary scripts
anymore.

Try and use Unicode variants of the Windows process creation API in
order to support filenames (and possibly environment) outside the
locale codepage.

WARNING: Implications on using Unicode environment are unknown.
It might affect the called process, or not, not sure.

Instead of fiddling with the "chcp" command in the generated batch
script on Windows, convert the whole script content into the system
codepage before executing it.

The working directory is passed in in UTF-8 encoding but Windows API expects
locale encoding here, so convert it.

Fixes #1076.

This drops the self-compiled 'grep' version which caused issues
with recursive searches on Windows as well as with non-ASCII
characters in paths.
The pre-compiled 'grep' binary from MSYS2 (matching the target ABI)
seems to solve probably all of the known problems on Windows.
The only drawback is that we need to ship a few additional MSYS2
libraries on which the 'grep' binary depends.

Closes #1229 and #1260.

* Update of Dutch transation.

* Update nl.po