Add support for signed word types.

[PeterCDMcLean]

Use logical shift right and avoid signed multiplication. Somehow builtin_popcount is also sensitive to sign

[codecov]

Codecov Report

Attention: Patch coverage is 76.51515% with 62 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
include/bitlib/bit-iterator/bit_details.hpp	65.97%	43 Missing and 6 partials ⚠️
include/bitlib/bit-algorithms/rotate.hpp	28.57%	5 Missing ⚠️
...de/bitlib/bit-algorithms/bit_algorithm_details.hpp	87.09%	0 Missing and 4 partials ⚠️
include/bitlib/bit-algorithms/find.hpp	76.92%	0 Missing and 3 partials ⚠️
include/bitlib/bit-algorithms/equal.hpp	83.33%	0 Missing and 1 partial ⚠️

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