Assert as-*'s arguments using defn prepost-map

[federkasten]

According to #17, I have refactored as-* function's argument validation using defn's prepost-map then addded more test cases for them.

[codecov]

Codecov Report

Patch coverage: 92.10% and project coverage change: -1.95 ⚠️

Comparison is base (2259d38) 96.35% compared to head (fe3b084) 94.40%.

❗ Current head fe3b084 differs from pull request most recent head c003dd5. Consider uploading reports for the commit c003dd5 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #19      +/-   ##
==========================================
- Coverage   96.35%   94.40%   -1.95%     
==========================================
  Files           5        9       +4     
  Lines         192      286      +94     
  Branches        3        4       +1     
==========================================
+ Hits          185      270      +85     
- Misses          4       12       +8     
- Partials        3        4       +1     

Impacted Files	Coverage Δ
src/cljc/proton/core.cljc	93.68% <92.00%> (-1.50%)	⬇️
src/cljc/proton/function.cljc	92.30% <92.30%> (ø)

... and 3 files with indirect coverage changes

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[iku000888]

LGTM