Fix some errors when vim is compiled with +python3.

When vim is compiled with `-python` and `+python3`, jedi-vim generates
errors because of two points in the code which are not compatible with
Python 3 (because of the `str`/`unicode` vs. `bytes`/`str` thing).
Merge pull request #135 from mlmoses/fix-python3-errors

Fix errors when vim is compiled with +python3.
Fix complete() deprecation.
Fix show_pydoc() get_definition() deprecation.
Fix get_definition() deprecation.
Fix goto() deprecation.
Fix related_names() deprecation.
Fix get_in_function_call() deprecation.
Fix goto() deprecation.
Merge pull request #138 from heavenshell/fix_deprecation_warning

Fix not to use deprecated method
Add whitespace after .
Merge pull request #140 from heavenshell/fix_pep8_violation

Add whitespace after =
Modify IndexError to LookupError in tabnew
Merge pull request #149 from gpoulin/lookuperror

Modify IndexError to LookupError in tabnew
Update README.rst

Correct documentation link text
Merge pull request #157 from twymer/patch-2

Update README.rst
remove a deprecated line
Merge branch 'dev' of github.com:davidhalter/jedi-vim into dev
changed contributing
removed an old description