Expand micro benchmarks

Replaces merge request !324 (closed). Closes #319 (closed). Work on expanding the scope of basic micro-benchmarks:

• Moved crypto context setup to header file lib-hexl-util.h
• Additional parameters for benchmarks run in lib-hexl-benchmark.cpp (parameters are in lib-hexl-util.h) e.g. Using scaling Ring Dimensions
• Macro introduced to abstract away benchmark parameters via Arg(s)(...) to single place in lib-hexl-util.h
• Additional benchmark operations: Subtraction, Negation, and Plaintext-Ciphertext Multiplication, Addition, and Subtraction.