Tidy up and fix enclosing paren detection in PSQ001.

Previously, we'd skip the first enclosing paren in statements like
"foo ((" which would cause the second matched paren to be marked
as too far away from "foo" whilst omitting the first paren.
Merge pull request #13 from smspillaz/common-universal-cmake.item_12

Consider the built-in typenames too.
Merge pull request #12 from smspillaz/common-universal-cmake.item_11

Tidy up and fix enclosing paren detection in PSQ001.
Add polysquare_add_checked_sources command.

This command allows a user to specify some sources which are not
considered a part of any target (say, for instance, installed headers)
and then run the static analysis checks over them like any other target.