Add ability to use custom delimiters

[annismckenzie]

This fixes #68 and introduces the ability to use custom delimiters.

Use like this:

var View = jet.NewHTMLSet("./views"))
View.Delims("[[", "]]")

<!-- file: "views/home.jet" -->
[[ extends "layouts/application.jet" ]]
[[ block body() ]]
  <main>
    This content will be yielded in the layout above.
  </main>
[[ end ]]

TODO:

• test extensively
• add documentation for it to the wiki

This fixes #68 and closes #98.

[jhsx]

we need to think a way to handle the comments also. We can bump the version for 3.0 and change the way comments work, per example an "*" after the delimiter would start a comment.

[annismckenzie]

For now, I'd stay away from a) making comment delimiters dependent upon the delimiter that's used and b) from bumping to v3 unnecessarily. The use case is to use Jet templates on the server in concert with Mustache-style template languages on the client side. Vanilla Mustache uses {{! }} for the comments so I think we're fine with {* *} which personally I haven't come across anywhere.

If and when we go ahead with #93, #84 and #32 we can talk about it again because for these I really do want to bump the major.

[annismckenzie]

I think this has reasonable coverage and will not break anything. I'll rework the Wiki slightly (it only mentions the Delims via this PR) and then go ahead and merge it.

[annismckenzie]

I updated the wiki: https://github.com/CloudyKit/jet/wiki/3.-Jet-template-syntax#delimiters