Feature/tf dataset adapter

[charlielito]

Adapter for handling tensorflow's tf.data.Dataset

[codecov-io]

Codecov Report

Merging #144 (338217f) into master (1a2fcc9) will increase coverage by 0.26%.
The diff coverage is 92.10%.

@@            Coverage Diff             @@
##           master     #144      +/-   ##
==========================================
+ Coverage   78.97%   79.24%   +0.26%     
==========================================
  Files         112      114       +2     
  Lines        5475     5589     +114     
==========================================
+ Hits         4324     4429     +105     
- Misses       1151     1160       +9     

Impacted Files	Coverage Δ
elegy/data/data_handler.py	72.41% <66.66%> (-0.43%)	⬇️
elegy/data/tf_dataset_adapter.py	86.00% <86.00%> (ø)
elegy/data/tf_dataset_adapter_test.py	100.00% <100.00%> (ø)

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[cgarciae]

@charlielito lets merge this before #139
Edit: On second thought, lets wait for #139 because it easier to fix the conflicts from this smaller PR than from that one.