improved error messages for "for" and "if" statements

[luchsamapparat]

Instead of the native JS error only the error message now also contains some context:

Before:

 Invalid or unexpected token

Now:

 Invalid or unexpected token:  (@@someVar=== true)

[coveralls]

Coverage decreased (-0.6%) to 82.234% when pulling 7e2d708 on luchsamapparat:master into 08ca093 on coderhaoxin:master.

[coveralls]

Coverage increased (+0.9%) to 83.756% when pulling b679664 on luchsamapparat:master into 08ca093 on coderhaoxin:master.

[haoxins]

v1.2.0 published :)

[luchsamapparat]

nice, thanks for the quick response!