Make delete a top level command

[eugeneius]

Most boom commands are passed as the first argument, with the list or item coming after:

boom urls github "https://github.com"
boom echo github
boom random urls
boom open github

Until recently, delete was an odd duck - it was passed after the list/item:

boom urls github delete #boo

As part of the 0.3.0 release, the syntax for deleting an item was changed to be less ambiguous:

boom github --delete #hmm

I think putting delete first, like all of the other commands, makes things even clearer:

boom delete urls github #yay

This is something I was considering a while ago, but I didn't want to break existing behaviour. Since 0.3.0 already did that, now is probably the best time to think about making this change.

[holman]

I was typing out a rebuttal to this but there's enough other counter-examples — boom open, etc — to where it makes sense. Let's do it.