Add support for NSIS 3.03, bug-fixes

[idleberg]

No description provided.

[Golmote]

Hi @idleberg! Thanks for contributing again!
Could you please not remove the ?: parts? They were intended, as all those captures are not required.
Only the two occurrences of (^\s*) are required to be captured for the lookbehind feature to work.

[Golmote]

You misunderstood me. The ?: should not be removed.

[idleberg]

I don't see which commit (prior to b490d6a) removed any ?:

[Golmote]

Hm... The global diff on the PR tells differently.
Are you working from an up-to-date branch? The ?: are in the current NSIS file, but are not in your first commit (a98c16b).

[idleberg]

You were right, my fork was not up-to-date. Closing in favour of #1288