clean up

[jonschlinkert]

• [ ] resolve or update issues based on latest release
• [ ] make a list of helpers that need to be documented
• [x] convert examples in docs that were copied over from template-helpers to be handlebars examples

[assemblebot]

@jonschlinkert Thanks for the issue! If you're reporting a bug, please be sure to include:

• The version of assemble you are using.
• Your assemblefile.js (This can be in a gist)
• The commandline output. (Screenshot or gist is fine)
• What you expected to happen instead.