Metadata and Solution interfaces - Multiple order of magnitude faster solution retrieval

[xtalax]

Adds metadata and solution interfaces

[codecov]

Codecov Report

Merging #154 (ce311a6) into master (0c6474c) will decrease coverage by 0.56%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master     #154      +/-   ##
==========================================
- Coverage   89.41%   88.84%   -0.57%     
==========================================
  Files          25       31       +6     
  Lines        1228     1390     +162     
==========================================
+ Hits         1098     1235     +137     
- Misses        130      155      +25     

Impacted Files	Coverage Δ
...ion/schemes/upwind_difference/upwind_difference.jl	88.23% <ø> (+0.35%)	⬆️
src/interface/MOLMetadata.jl	0.00% <0.00%> (ø)
src/interface/solution/common.jl	65.11% <65.11%> (ø)
src/interface/solution/timedep.jl	90.00% <90.00%> (ø)
src/MOL_discretization.jl	82.81% <100.00%> (+0.69%)	⬆️
src/MOL_utils.jl	82.97% <100.00%> (+0.12%)	⬆️
src/interface/solution/MOLMetadata.jl	100.00% <100.00%> (ø)
src/interface/solution/solution_utils.jl	100.00% <100.00%> (ø)
src/interface/solution/timeindep.jl	100.00% <100.00%> (ø)
src/error_analysis.jl	11.11% <0.00%> (-0.89%)	⬇️
... and 11 more

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[xtalax]

@ChrisRackauckas Everything passing except invalidations, is this ok to merge?