[Geany] integrating external tools (e.g. lint)

[AC]

> error_regex=^(.+?):([0-9]+):[0-9]+

Now I'm confused - that works.
But all you added was the last bit (and the caret, which is not relevant here
though). As I understand it (and testing in Python and JavaScript confirms
this), the non-greedy indicator should render that last part obsolete!?
While this seems somewhat off-topic, it might confuse other users as well.