Don't set 'markdown' filetypes for txt files

We don't really want to have 'markdown' filetype in all Fugitive service
buffers.
Add mapping to copy text without linebreaks.

And removed the old crappy one
Fix CtrlP ignoring all 'doc[anything]/' folders

Actually I wanted to ignore just 'doc/' folder, which contains generated
rdocs in Rails projects.
Fix swapped resize window up/down 'J' and 'K' maps