Update powerline for new psutil

Fixes #835
Switch comments
Fix tests for new psutil
Merge pull request #838 from ZyX-I/new-psutil-fixes

New psutil fixes
Put _powerline_prompt at the start

Reason: $? may be overridden by the previous commands in PROMPT_COMMAND that do 
not keep it like _powerline_prompt does (see `return $last_exit_code`). 
(@ascrane)

Closes #836
Merge branch 'bash-keep-status' into develop
Fix flake8 complaints
Add ellipsis argument to cwd segment
Document istime date argument
Add fuzzy_time(unicode_text) argument
Suggest URIs under query_url description
Merge pull request #840 from ZyX-I/review-res-fixes

Fixes #819.
Add fix for old vims

Old vim versions did not support both unicode() and str() in python2 bindings in 
a number of places.

Fixes #829
Do not use :redrawstatus!: it makes intro disappear

It seems that old fix for old code is no longer needed. At least I do not see 
any problems with

    vim -u NONE -S ~/.vam/powerline/powerline/bindings/vim/plugin/powerline.vim --cmd 'set ls=2'

.

Fixes #250
Merge branch 'fix-intro' into develop
Merge remote-tracking branch 'author/develop'