Add "ByScalar" to shift operations

Rename the shift operations to include "ByScalar" to clarify that their
shift count is a scalar value, and to make namespace room for adding
vector-vector shifts in the future.
Testcases for shifts.

Add tests for shiftLeftByScalar, shiftRightArithmeticByScalar, and
shiftRightLogicalByScalar.
Merge pull request #87 from sunfishcode/shiftByScalar

Shift by scalar