Currently, handling of URI escapes is ad-hoc; escaped strings are
stored as-is in the URI structure, and it is up to the individual
protocol to unescape as necessary. This is error-prone and expensive
in terms of code size. Modify this behavior by unescaping in
parse_uri() and escaping in unparse_uri() those fields that typically
handle URI escapes (hostname, user, password, path, query, fragment),
and allowing unparse_uri() to accept a subset of fields to print so
it can be easily used to generate e.g. the escaped HTTP path?query
request.

Signed-off-by: Joshua Oreman <oremanj@rwcr.net>
Signed-off-by: Marty Connor <mdc@etherboot.org>