Better support for AbstractString

[devmotion]

Fixes #396.

[codecov]

Codecov Report

Base: 83.76% // Head: 83.76% // No change to project coverage 👍

Coverage data is based on head (2146275) compared to base (8c3f5ed).
Patch coverage: 66.66% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #397   +/-   ##
=======================================
  Coverage   83.76%   83.76%           
=======================================
  Files          19       19           
  Lines        1035     1035           
=======================================
  Hits          867      867           
  Misses        168      168           

Impacted Files	Coverage Δ
src/chains.jl	84.39% <57.14%> (ø)
src/utils.jl	95.29% <100.00%> (ø)

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 at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[cpfiffer]

Thanks!