Tab completion improvements

[certik]

I am collecting all tab improvements issues into this master issue:

• The auto completion does not escape characters #176
• Make tab completion work for cd C:\Users (add ' automatically) #31
• Tab completion for hidden files .<TAB> does not work #249
• Add git tab completion #80
• Tab completion with spaces does not work #177
• Tab completion for cd should only show directories #199
• Tab completion of a single option should add a space at the end #191
• Tab completion doesn't work for some executables in PATH #190
• "sou<TAB>" completes to sourcekit-lsp instead of source #193
• Tab completion for executables should only show executables #202