geanylatex: fix automatic capitalization of multi-byte characters

Fix indexing relative document positions by characters, not bytes, when
performing automatic capitalization of sentence start.

Geany API dependency is bumped to 217.  Even though this change doesn't
actually require new API introduced by this version, it requires
Scintilla 3.3.5 which is only available in Geany 1.24, and API 217 is
the closest one to this.
geanylatex: Allow for multiple spaces after punctuation when capitalizing

Allow form multiple white spaces (including newlines) after a
punctuation when checking whether to capitalize the sentence start.

This is useful because some people are used to write two spaces between
sentences, and it also allows to capitalize the first sentence of a new
paragraph.
Merge pull request #143 from b4n/geanylatex/extended-chars-capitalization

Geanylatex: extended characters capitalization