Merge pull request #5 from gMagicScott/bug/4

Include WordPress file for `is_plugin_active` on frontend
Add contributers, and license information to readme
Add additional fields to TinyMCE button dropdown
Fix PHP undefined variable error
Fix spelling and permissions on admin page
Fix spacing
More spacing
Remove note about textarea shortcode
Correct admin menu link
Plugin settings security
Create .travis.yml
Update NOTES.md
No email notifications from Travis

At this time in this repo's history, email notifications from Travis-CI are overkill. Perhaps we will turn them back on in the future.
Have [switch] match uppercase

Since WordPress converts all shortcode attributes to lowercase during
processing, our shortcode will never match uppercase letters in either
the $_GET or $_POST globals.

After checking that the field exists, it needs to be run through
`strtolower()` to have at least a “Case Insensitive” match.

This issue should be revisited later to make the match
“Case Sensitive,” but that may require modification to WordPress Core.

[Addresses: GH-12]
Display content based on request variables

There was a feature request to be able to nest shortcodes inside of
the existing shortcode `[switch]`. This is not possible without
overriding large portions of WordPress core. In speaking with that
customer, we came up with the content for `[block]`

[Addresses: GH-8]
Display merge default when `$request` is empty

When the `$_REQUEST` super global has a key set without a value the
merge shortcode returns that empty value. Generally this is not
desired.

This is especially prevalant with `$_GET` variables coming from an
autoresponder email. `http://example.com/page/?Name=%$name$%` and more
is hardcoded in. When 1ShoppingCart fills the merge on their end,
those fields merge nothing if the value doesn't exist for the customer.

When that is the case, the specified default text should be displayed.

[Addresses: GH-7]
Merge pull request #7 from gMagicScott/MT-request-merge

Default merge codes not displaying with empty merge field
Merge pull request #12 from gMagicScott/switch-match-upper

Switch shortcodes should match uppercase variables
Merge pull request #8 from gMagicScott/feature/block-shortcode

Nest additional shortcodes in `[switch]`
Custom fields for Chris Cool