rename from camel to snake case

[TSchiefer]

• rename swcGetMapping() and swcGetMutations() to swc_get_mapping() and swc_get_mutations()
• soft-deprecated the old functions
• updated tests
• removed file with example output (kind of outdated and didn't seem to be so useful)

closes #8

[codecov[bot]]

Codecov Report

Merging #15 into master will decrease coverage by 3.4%. The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master      #15      +/-   ##
==========================================
- Coverage   87.79%   84.38%   -3.41%     
==========================================
  Files           2        3       +1     
  Lines         254      237      -17     
==========================================
- Hits          223      200      -23     
- Misses         31       37       +6

Impacted Files	Coverage Δ
R/swcGetMutations.R	98.33% <ø> (-0.24%)	:arrow_down:
R/swcGetMapping.R	81.92% <100%> (-1.77%)	:arrow_down:
R/aaa-function.R	45.45% <45.45%> (ø)

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[krlmlr]

Squash-merged, thanks!