Match a string literal exactly
| Name | 
|---|
| value_type | 
| Name | Description | 
|---|---|
| literal_rule[constructor] | Construct from char | 
| parse | 
If there is no more input, or if the end of the input is reached, and a prefix of the literal matches exactly, the error returned is error::need_more.
using value_type = core::string_view;
Rules are used with the function parse.
system::result< core::string_view > rv = parse( "HTTP", literal_rule( "HTTP" ) );