Bugfix/364 reconstruction update start symbol of parser instead of recreating it

load_grammar now collects all imports to make before loading them to …

Run tests against Python 3.7 and pypy 6.0

import_grammar now include base_path in recursive call to load_grammar

get_namespace_name now preserves leading underscore on relative import

Fix v_args when used on classes with non-callable members

Add test data files to MANIFEST

Needed for tests to succeed on a packaged version of lark.

Include relative imports and rule rewrite

%import .local.foo -> bar

The `.` character is invalid as a group name in regex, replacing by `__`.
The bug arose in `lexer._build_mres`.

%import common.NUMBER -> N
%import .local.NUMBER -> N