This adds Lua hooks to CryptManager for libtomcrypt's SHA256 hash
function. It follows along with the C++ patterns Glenn wrote a decade
and a half ago for CryptMananger's MD5 and SHA1 hooks.
StepMania's CMakeProject-tomcrypt file has been updated to build with
sha256 symbols. Invoking cmake to build with system tomcrypt works fine
as-is.
Note that these functions return binary formatted strings, but themers
can convert to hexadecimal format using the global Lua function
BinaryToHex().