Better shell syntax

[bmatsuo]

I basically wrote the easiest thing that would give me what I needed. There are issues with it that need to be addressed.

• [x] The '+' character is not good for its purpose. It is a common character in URLs and in those cases bad things happen (resolution: this is actually ok as long as its behavior is restricted only to spots where it is the first character following a space, which excludes urls; i think the semantics are more obvious than other symbols like %, @, etc).
• [X] The lack of quoting and escaping doesn't appear to be immediately pressing (assuming '+' is changed). But that is probably pretty short sighted. edit: It is short sighted. The "pipe" command is a little cumbersome without quotes, but it also takes advantage of not needed quote nesting. The two cases need to be handled. Quoting is part of that (resolution: I will create a new ticket for quote support; it will not be in the 0.5 release).
• [x] It's not clear if the idea of prefixing commands with a colon was the right choice. Common usage should dictate wether the "push" shorthand remains. edit: it may also be more convenient to make "peek" the default semantics (resolution: after using the tool some more I think the shorthand semantics are correct; things will make this easier like being able to see the filter in the prompt text #21).

[bmatsuo]

TL;DR -- After getting my hands dirty with the most recent APIs I think the only thing that really needs to change is support for quoted strings. This is not super critical. I will write a simple scanner using the library I used to scan jq version strings.

But we can get on with the 0.5 release. Yay!