Clean up STPL voodoo

Rewritten to use:

- Raw strings
- Triple-quoted strings
- Verbose regex mode `(?x)`

Also includes a fix changing `[urbURB]?` to `[urbURB]*` to match `ur'test'`
Prevent syntax errors when line-wrapping comprehensions

Ignores block keywords inside parentheses/braces/brackets, allowing
list/set/dict comprehensions to be wrapped in the same way as dicts. Does not
check for correctly paired parentheses - we can let python do that, right?

Builds upon cleanup made in https://github.com/bottlepy/bottle/pull/689
Merge pull request #690 from eric-wieser/stpl-comprehensions

Stpl comprehensions