[boost] Ann: guid library

I have uploaded a new version of the guid library to the boost vault (guid_v4.zip). (I seem to be unable to change the file description for guid_v3.zip to not say the last version.) Changes: I have written documentation. The create function now just creates a random number based guid instead of pretending to create a time-based one. It uses Boost Build System V2 I plan to add serialization and name-based creation in the near future. I welcome any (and hope to receive many) comments and criticisms. Andy Tompkins