web/explain: bind left/right arrows to navigate between groups (fixes #50)
matcher: print all matches in debugmatch
store: add support for nested commands
matcher: add support for nested commands (fixes #18)
matcher: add support for nesting through flags
matcher: add support for ending a nested command with an argument
parser: allow visiting the end of a simple command

The return value of visitcommand is passed into visitcommandend. This makes it
easier to assosciate the two.
es.js: fix initialize to work with multiple commands and no shell groups
views/debug: allow editing the nestedcommand field
matcher: don't fail prematurely if a partialmatch is unsuccessful
views: strip the command