Use better hashing in cache key calcuation

[t-b]

Using StringCRC is actually quite bad for calculating a hash of the data, as 1 states

CRC-32 poses the highest risk for hash collisions. This hash function is generally not recommended for use. If a hub were to contain 77,163 hash values, the chance of a hash collision occurring is 50%, which is extremely high compared to other methods.

AllenInstitute/mies-utils-xop#1 has a WIP branch with XXH32 from 2 which has the following performance characteristics.

Function dostuff()

	variable ref, i, numLoops = 1e5
	string str = "abcdefghijklmnopqrstuvwxyz"
	str = ReplicateString(str, 10)
	variable result
	string resultStr
	
	ref = stopmstimer(-2)
	for(i = 0; i < numLoops; i += 1)
		result = StringCrC(0, str)
	endfor

	printf "CRC32:    %.15d, time: %f micro seconds\r", result, (stopmstimer(-2) - ref) / numLoops

	ref = stopmstimer(-2)
	for(i = 0; i < numLoops; i += 1)
		result = MU_CalcHash(str, 0)
	endfor

	printf "XXHash32: %.15d, time: %f micro seconds\r", result, (stopmstimer(-2) - ref) / numLoops

	ref = stopmstimer(-2)
	for(i = 0; i < numLoops; i += 1)
		resultStr = Hash(str, 3)
	endfor

	printf "MD5:      %.15s, time: %f micro seconds\r", resultStr, (stopmstimer(-2) - ref) / numLoops

	ref = stopmstimer(-2)
	for(i = 0; i < numLoops; i += 1)
		resultStr = Hash(str, 1)
	endfor

	printf "SHA256:   %.15s, time: %f micro seconds\r", resultStr, (stopmstimer(-2) - ref) / numLoops
End

gives

•dostuff()
  CRC32:    000001268438376, time: 0.198013 mikro seconds
  XXHash32: 000001044162042, time: 0.467863 mikro seconds
  MD5:      4e6405697346169, time: 1.934640 mikro seconds
  SHA256:   6f6a4460cbd9241, time: 5.233524 mikro seconds

so while a tiny bit slower than CRC32 this is much faster as the other hash algorithms.

Adding this new hash would also allow us to move to XXhash from SHA* where we don't need cryptographic hashes.