Fix fieldnames bug in AtomsBase interface

[ejmeitz]

Realized fieldnames was called on the system instance not the typeof the system which is not right.

[ejmeitz]

How do I change the SimpleCrystals compat to be just 0.1.5?? I changed stuff in 0.1.6 that broke a test here.

[jgreener64]

= 0.1.5 but better to fix the test and up the compat to 0.1.6?

If you are following semver with that package you should also bump to 0.2.0 if there are breaking changes.

[ejmeitz]

Yeah I'll fix them, you mind if I just add that in this PR?

I didn't actually change the interface. The way I coded it in Molly just didn't use the interface (oops). I accessed a property directly (atom.sym) but I changed it to atomic_symbol in 0.1.6. I should just be calling the atomic_symbol function.

[jgreener64]

Yes add it to this PR.

[codecov]

Codecov Report

Patch coverage: 75.00% and project coverage change: -0.06 ⚠️

Comparison is base (58d3390) 73.37% compared to head (5a672de) 73.31%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #145      +/-   ##
==========================================
- Coverage   73.37%   73.31%   -0.06%     
==========================================
  Files          34       34              
  Lines        5022     5022              
==========================================
- Hits         3685     3682       -3     
- Misses       1337     1340       +3     

Impacted Files	Coverage Δ
src/types.jl	72.60% <75.00%> (ø)

... and 1 file with indirect coverage changes

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[ejmeitz]

Ok changes made, no clue why the agent tests fail in one of the test sets and pass in the others.