BUG: Fix for #1487

The parser could sometimes generate invalid code if the
source-file-comments were enabled, this moves the comments outside the
html-tag to circumvent these problems, update test as well.
Merge pull request #1726 from s-m/1487-fix-template-comments

BUG: Fix invalid code with source-file-comments, fixes #1487
removing potentially invalid html in email

The generic email template encapsulates the "body" content in a paragraph mark.  This is undesirable as it can lead to invalid HTML. Rather than using a paragraph, it is better to have a div encapsulating the content.

The underlying reason for this is that $Body is usually HTML and this can included block elements (div, p, etc...) that are not allowed within paragraphs (p).

It is important that the HTML is valid, because it will reduce the likelihood for it being marked as spam, because it is less likely to show up strange formatting and for use of tools like emogrifier.
Extended docs for shortcode handling and doctypes (fixes #1700)
Remove duplicate functionality between float and double
Merge pull request #1769 from wilr/doubleduplication

Remove duplicate functionality between float and double
Enforcing extension-less file validation (fixes #1767)

By default, File.allowed_extensions contains '' (no extension),
but if you specifically remove it, the validation should pick it up.
BUG: HiddenFields and VisibleFields should always return extraFields

HiddenFields() and VisibleFields() should always return extraFields, e.g. HiddenFields doesn't return SecurityID if it is called before Fields().
BUG HTTP will now correctly pass over mailto: links when converting relative links to absolute (e.g. in Emails)