Deal with (x; y=0) -> ... pattern

[pablosanjose]

Closes #8

Before this PR, the kwarg y=0 in splitdef((x; y=0) -> ...) was being injected as :(y=0) instead of Expr(:kw, y, 0) into the Dict. This fix is done via special-casing this pattern.

[codecov]

Codecov Report

Merging #9 into master will increase coverage by 1.35%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
+ Coverage   94.93%   96.29%   +1.35%     
==========================================
  Files           2        2              
  Lines          79       81       +2     
==========================================
+ Hits           75       78       +3     
+ Misses          4        3       -1     

Impacted Files	Coverage Δ
src/function.jl	96.25% <100.00%> (+1.37%)	⬆️

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[oxinabox]

thanks!