Adding relative import support (#60)

* Changing the `all_imported_modules_in_file(self, file)` projection in build which gathers imports from file ASTs root nodes.
* Adding support for the relative import syntax in noderepr.py and output.py.
* Adding a relative counter int to the AST nodes and fixing up treetransform.py.
* Changing the `parse_import_from(self)` function to parse relative imports.
Fixing issues with semantic analysis of relative imports (#60).

* Cleaning up and adding relevant tests.
Merge branch 'master' of https://github.com/mason-bially/mypy into mason-bially-master
Fix import targeting the current module

Fixes #518.
Add relative import test case
Remove end-of-line whitespace
Add relative import test cases
Add test cases
Update relative import error messages
Add relative import test cases
Add relative import test cases
Merge branch 'mason-bially-master'

Note that I added some tests and did a few fixes/tweaks.
Fix Python 2 by removing 'print' as a keyword
Fix parser bug
Fix Python eval test runner

Also do some refactoring.
Add type annotation to fix type error