Attach source information to read errors
Improve error reporting for read errors

Print read errors with as good source location as possible.  For
premature end of file, try extra-hard to find good source position by
explicitly scanning for unbalanced parenthesis.

See #76
Merge branch 'improve-error-reporting'

* improve-error-reporting:
  Improve error reporting for read errors
  Attach source information to read errors

Conflicts:
	cask.el