Clarify use of unit ranges in multiple-bit functions

[Borketh]

Resolves #7

[codecov]

Codecov Report

Merging #8 (1048a0c) into master (253cd0b) will decrease coverage by 0.78%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
- Coverage   60.78%   60.00%   -0.79%     
==========================================
  Files           4        3       -1     
  Lines          51       50       -1     
==========================================
- Hits           31       30       -1     
  Misses         20       20              

Impacted Files	Coverage Δ
src/BitOperations.jl

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[oschulz]

Thanks!

[oschulz]

JuliaRegistries/General#43337