Replace trim methods with RegExp

[fatfisz]

This PR does two things:

• Add "start" and "end" sides for trimResultTransformer - this is in line with string methods already in the standard (like padStart/padEnd) and with the stage 2 proposal trimStart/trimEnd.
• Because trimLeft/trimRight (or their start/end counterparts) are not yet a part of the standard, they are replaced in the code with regular expressions.

[codecov-io]

Codecov Report

Merging #127 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #127   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          23     23           
  Lines         150    152    +2     
=====================================
+ Hits          150    152    +2

Impacted Files	Coverage Δ
src/trimResultTransformer/trimResultTransformer.js	100% <100%> (ø)	:arrow_up:
...c/stripIndentTransformer/stripIndentTransformer.js	100% <100%> (ø)	:arrow_up:

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