Fix sentence splitter: sentences ending with acronyms

[nickto]

A sentence ending with an acronym was dot distinguished from an initial
followed by a period in the middle of the sentence. E.g., "Adamson is not from USA.
They are from Europe" was considered as a single sentence because "USA." was
treated as an initial.

1. Added a requirement for the initial to be only one letter long: "A." in "A.
   Adamson" is still treated as an initial, while "USA" in "from USA. They" is not.
2. Added a test for such case.

[codecov-io]

Codecov Report

Merging #24 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #24   +/-   ##
=======================================
  Coverage   80.86%   80.86%           
=======================================
  Files           9        9           
  Lines         277      277           
=======================================
  Hits          224      224           
  Misses         53       53

Impacted Files	Coverage Δ
src/sentences/sentence_splitting.jl	88.13% <100%> (ø)	⬆️

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[oxinabox]

Good catch, do you think it would be better use use \b rather than \s ?
\b is word-boundry, where as \s is white-space.
I think \b would work better if at the start of the string,

[nickto]

Good catch, do you think it would be better use use \b rather than \s ?
\b is word-boundry, where as \s is white-space.
I think \b would work better if at the start of the string,

Changed it to \b and added a test that fails when using \s, thanks!

[oxinabox]

LGTM, will merge when tests pass

[oxinabox]

thank!