Add a for .. from .. loop for generators, see #4306, #3832 (#4355)

* Added support for for-from loop, see #3832

* for-from: remove extra newline and add support for ranges

* for-from: tidy up the lexer

* for-from: add support for patterns

* for-from: fix bad alignment

* for-from: add two more tests

* for-from: fix test "for-from loops over generators"

See explanation here: #4306 (comment)

* for-from: delete leftover console.log

* Refactor the big `if` block in the lexer to be as minimal a change from `master` as we can get away with

* Cleanup to make more idiomatic, remove trailing whitespace, minor performance improvements

* for-from: move code from one file to another

* for-from: clean up whitespace

* for-from: lexer bikeshedding

* Move "own is not supported in for-from loops" test into error_messages.coffee; improve error message so that "own" is underlined

* Revert unnecessary changes, to minimize the lines of code modified by this PR