Use colon as default ID separator

[jonaskello]

Fixes #42

[codecov]

Codecov Report

Merging #43 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #43   +/-   ##
=======================================
  Coverage   87.24%   87.24%           
=======================================
  Files           6        6           
  Lines         196      196           
  Branches       49       49           
=======================================
  Hits          171      171           
  Misses         12       12           
  Partials       13       13

Impacted Files	Coverage Δ
src/functions.ts	83.07% <ø> (ø)	⬆️

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