- cache current environment
- s/jedi.get_python_environment/jedi.get_system_environment: the former
does not exist (renamed in https://github.com/davidhalter/jedi/commit/336087f)
- improve error display
This basically corrupts VIM's Python, because it might be having a differnet prefix (Python 3.6) than sys path. I don't know who came up with this - probably it's just how Python loads venvs - but it's definitely not good. Fortunately we can just reset it and be happy.
Unlisted buffers might come e.g. from `set viminfo+=%`, and Jedi would
crash on them.
This could additionally check for them to be readable, but this should
be handled in Jedi itself anyway.
Move jedi_vim.py and the jedi submodule into pythonx, which gets added
to Vim's internal sys.path. While jedi cannot be imported directly from
there, it still makes sense for consistency.