Select to matching brace

The feature of jumping in between braces is really useful. Often I find me wanting to select the text in between braces. So I added the feature to geany.

The default keybinding I used is Ctrl-Shift-B because Ctrl-B goes to the matching brace.

geany.txt is updated for documentation.

removed TODO tag
Merge branch 'Select_Matching_Brace' of https://github.com/firebirdberlin/geany into Select_Matching_Brace