First changes for adding big endian support

See issue #18.
Fix some variable types
Make msrpc_rts_pdu_len() data representation (endianess) aware
Make msrpc_pdu_get_rts_pdu() data representation (endianess) aware
Make msrpc_rts_pdu_get_command_name() data representation (endianess) aware
Make msrpc_rts_get_virtual_channel_cookie() data representation (endianess) aware
Merge branch 'big_endian_support'

This adds support for big endian platforms and fixes #18.