Support for Other inputs types besides Text

The Problem: Co-Authors-Plus Guest-Authors Profiles are very limited. If you want to expand on a existing Group ("Constact Fields") You can only use Text input types.

The Solution: A field item called Input that declares the field's type. This would be assumed by default to be text, and the existing, "hidden", "email" and "website" fields would be assigned the standard "hidden", "email" and "url" input types. 

In addition, for someone who may not want to website field to be forced to a real URL, a filter would be applied to each field's input to allow it to be override, without pulling all fields via "coauthors_guest_author_fields" filter.

The new filter would look something like this `$pm_key_input`. So to change Website back to text would be `apply_filter('cap_website_input', 'myfunction_that_returns_text');`

Does not yet support:
Select
MultiSelect
Radio (Easily)

Adds Support for:
Checkbox
Url
Email
Number/date fields
Better Checkbox Support

Added Support For Checkboxes to save and show the correct info. After #123 this is now easily.
Fix for checkboxes
Update class-coauthors-guest-authors.php

Should Meet WordPress coding Standards now. Adjusted, filter names to prefix with CAP-, also they are section & field specific. 

Test of the filter and adding a new field (checkbox)
https://gist.github.com/alpha1/9421107

limitations:
radio buttons likely do not work.
select/multi select will not work.
Textareas do not work. 

Only inputs that are similar to a test field, like email will work. Checkboxes also work.

I'll be happy to work towards supporting all of those in the future.
Don't show the "Create Profile" link by default

Outside of WordPress.com, creating site-specific user profiles is less common of a use case. Having a "Create Profile" link just causes confusion.

However, if the user already has a mapped profile, we'd still like to show that link.
Don't show the guest author links at all in the network admin

Fixes #181
Readme update
Merge pull request #185 from Automattic/no-show-profile

Breaking change to "Create Profile" link
Merge pull request #156 from alpha1/master

Guest-Authors Need Support for Other Input types than "text"