Massive update making DRWMutex compatible with sync.rwmutex again and more

[fwessels]

Massive update making DRWMutex compatible with sync.rwmutex again and more (in order of importance)

drwmutex.go / drwmutex_test.go:

• DRWMutex made compatible with sync.rwmutex (via writeLocks & readersLocks arrays) so it now allows multiple RLocks() to be done on the same object
• Refactor out common code for Lock/RLock and Unlock/RUnlock
• Added full test harness from sync.rwmutex
• Added benchmarks from sync.rwmutex
• Unlock()/RUnlock() on unlocked object will panic (conform sync.rwmutex)

dsync_test.go:

• Use simple int64 instead of []bool for DRWMutex book keeping (map[string]int64 instead of map[string][]bool)

other changes:

• Updated README.md (still WIP)
• Add chaos/\ sub-dir that will test additional edge cases

[harshavardhana]

Looks like the branch has conflicts @fwessels

[fwessels]

Closing and submitting new one