Allow for sending data

[LVala]

Additionally, modify the examples to create a media loop (browser -> Elixir PeerConnection -> browser).

[codecov]

Codecov Report

Merging #21 (0d0a0f7) into master (16043e7) will decrease coverage by 4.27%.
The diff coverage is 47.88%.

❗ Current head 0d0a0f7 differs from pull request most recent head e8cef4e. Consider uploading reports for the commit e8cef4e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #21      +/-   ##
==========================================
- Coverage   84.05%   79.78%   -4.27%     
==========================================
  Files          10       10              
  Lines         483      475       -8     
==========================================
- Hits          406      379      -27     
- Misses         77       96      +19     

Files	Coverage Δ
lib/ex_webrtc/media_stream_track.ex	100.00% <100.00%> (ø)
lib/ex_webrtc/rtp_transceiver.ex	92.30% <100.00%> (-0.29%)	⬇️
lib/ex_webrtc/dtls_transport.ex	80.00% <42.10%> (-5.37%)	⬇️
lib/ex_webrtc/peer_connection.ex	72.41% <48.00%> (-7.38%)	⬇️

... and 1 file with indirect coverage changes

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