[GCheckSum] Add CRC checksumming
@sdroege
Submitted by Sebastian Dröge Link to original bug (#523149)
Description
Hi, it would be nice if GCheckSum would offer CRC and Adler algorithms for checksumming too.
See http://en.wikipedia.org/wiki/Cyclic_redundancy_check and http://en.wikipedia.org/wiki/Adler-32
Implementing them should be almost trivial, it would only mean to add many new GChecksumTypes and maybe a G_CHECKSUM_CRC_CUSTOM & g_checksum_set_crc_polynomial() for using a custom polynomial.