Expose CURLPROTO_* values in protocols table

Add a table "protocols" in the module with protocol names as keys and
CURLPROTO_* defines from curl.h as values. Those values are meant to be
used with the bit32 module in lua 5.2 and with Lua BitOp in lua 5.1 and
luajit.

Exposing protocol values is the first step toward adding support for
CURLOPT_PROTOCOLS and CURLOPT_REDIR_PROTOCOLS from curl_easy_setopt.

Signed-off-by: Davide "FunkyAss" Del Zompo <davide.delzompo@gmail.com>
setopt: support PROTOCOLS and REDIR_PROTOCOLS

The second argument of both the new functions, setopt_protocols and
setopt_redir_protocols, is a number representing a bitmask of protocols
(see libcurl documentation for curl_easy_setopt).

Signed-off-by: Davide "FunkyAss" Del Zompo <davide.delzompo@gmail.com>
Merge pull request #9 from FunkyAss/protos

Add support for CURLOPT_PROTOCOLS and CURLOPT_REDIR_PROTOCOLS