fix#257
This fixes a problem when doing split parsing (header then body).
The problem arises when the first buffer passed to the header
parser contains exactly the full header and nothing more. The
symptom is that when parsing the body, the parse will erroneously
be considered complete.
fix#171
Several names and HTTP identifiers are renamed to be
more consistent, self-explanatory, and concise:
* "Fields" is a collection of HTTP header fields (rfc7230 section 3.2)
* "Header" is the Start Line plus Fields. Another way to look at it is,
the HTTP message minus the body.
* `basic_fields` replaces `basic_headers`
* `fields` replaces `headers`
* `Fields` replaces `Headers` in template parameter lists
* `header` replaces `message_headers`
* `header::fields` replaces `message_headers::fields`
The changes are cosmetic and do not affect run-time behavior.
message_headers is now a set of partial class template
specializations instead of a template class alias. This solves
a problem where template functions taking message_headers as a
parameter could not deduce argument types, since std::conditional
obscured the deduced context.
Both classes are refactored to share declarations using an #ifdef,
to eliminate an ugly set of extra declarations needed when building
the documentation.
Copy and move class special members are added.
A new function message::base() is provided which returns the
message_headers portion of a message.
Vinnie Falco