Add global gitignore, update tmux-navigator.

Add:
	gitconfig, git/gitignore
		-Add global gitignore file (currently only for my ".vimrc.local" files).

	vim/bundle/vim-tmux-navigator
		-update submodule to latest commit.

	sshconfig
		-Add bithshift ssh information.
Refactor zsh*; add gdsu(), cc(). Add alt-ftplugin.

Add:
	vimrc_after
		-make all function calls `silent!`, to suppress obtrusive messages and
		occasional confirmation prompts.

	zshrc
		-add cc(), to compile a `c` source file into an executable
		with an identical root filename.
		-add gsdu(), to painlessly delete a submodule.

Ref, Rem:
	zshrc, zsh/oh-my-zsh.zsh
		-migrate oh-my-zsh configuration directives from zsh/oh-my-zsh.zsh to
		zshrc, and remove oh-my-zsh.zsh.