Add a few configuration-related features

[mortenpi]

I figured I'd PR these separately from the documentation for easier review.

[codecov[bot]]

Codecov Report

Merging #30 into master will increase coverage by 0.5%. The diff coverage is 100%.

@@            Coverage Diff            @@
##           master      #30     +/-   ##
=========================================
+ Coverage   89.71%   90.22%   +0.5%     
=========================================
  Files          15       15             
  Lines         700      716     +16     
=========================================
+ Hits          628      646     +18     
+ Misses         72       70      -2

Impacted Files	Coverage Δ
src/configurations.jl	99.24% <100%> (+0.85%)	:arrow_up:

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[jagot]

Thanks!