This should have been done a *long* time ago, back when I initially
added Websocket support. This is the first part of two in improving
loop handler support with regards to socket closure.
Reason may include: {normal, shutdown} for the most normal shutdown,
{normal, timeout} for a loop handler timeout shutdown, or {error, _}
if an error occured.
Header names are now binaries. Since header names are case insensitive
they are all converted to lowercase. For example: <<"content-length">>.
The max_line_length option was removed. Three new options have been
added instead:
* max_request_line_length (defaults to 4096)
* max_header_name_length (defaults to 64)
* max_header_value_length (defaults to 4096)
These functions allow to set response headers and body in advance,
before calling any of the reply functions.
Also add has_resp_header/2 and has_resp_body/1 to check if the given
response headers have already been set.
