Add http_argument_urldecode() which takes a string and decodes any url encoding done to it.

Change kore_strtonum() to pass 0 to strtoll by default so we can use it to convert hex numbers (prepended with 0x) as well.
and as always, remove debug.
Pass the base for strtoll() to kore_strtonum(), breakage ensues if we depend on the "auto" detection that happens when we pass 0 to strtoll() as base.
add cb_extra to http_requests so its a bit easier to pass certain data between handler functions (kore won't touch cb_extra).
set cb_extra to NULL when req is allocated
cb_extra -> hdlr_extra and add one to struct connection as well for persistent data across requests.
free hdlr_extra if its set
Add reason phrases and http status constants (HTTP_STATUS_* see includes/http.h)
Based on work from mendor/ymv via github.
Merge branch 'master' of github.com:jorisvink/kore