`gg` moves to the first non-blank character on the line
`G` moves to the first non-blank character on the line
Move `:q<Enter>` tests to avi.command-line-mode-test
`:3` moves to line 3
Extract command-line-mode/line-number?
Extract command-line
Nest threading macros
Use cond to avoid multiple match problems
`:<Enter>` does nothing
`:badcommand<Enter>` doesn't change the cursor position
characters typed after `:` canbe deleted with backspace
Treat DEL as <BS> for now (because Mac)
Merge remote-tracking branch 'gcapizzi/master'

Conflicts:
	src/avi/normal_mode.clj
<BS> at position zero on the command-line cancels
`ixxx<Esc>` inserts three xs
`ixyz<Esc>` inserts `xyz`
Extract b/insert-text
`<Esc>` in insert mode goes to normal mode
Display --INSERT-- on the prompt line when in insert mode
Fix test verbiage