Add behaviour and dynamic dispatch for (de)payloaders

[sgfn]

Closes #143

[LVala]

I'm a bit unsure about adding specs to callback implementation. I believe that ex_doc will generate the spec anyway (based on the callback) and making the callback and implementation spec different is a big yucky, but on the other hand, we know that e.g. Opus.depayload will never return {nil, depyayloader}. I'm a bit torn when it comes to this.

[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.51%. Comparing base (af1fec4) to head (b142d04).
Report is 4 commits behind head on master.

Files	Patch %	Lines
lib/ex_webrtc/rtp/vp8/depayloader.ex	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #147      +/-   ##
==========================================
+ Coverage   88.31%   88.51%   +0.20%     
==========================================
  Files          36       38       +2     
  Lines        1891     1907      +16     
==========================================
+ Hits         1670     1688      +18     
+ Misses        221      219       -2     

Files	Coverage Δ
lib/ex_webrtc/rtp/depayloader.ex	100.00% <100.00%> (ø)
lib/ex_webrtc/rtp/opus/depayloader.ex	100.00% <100.00%> (+100.00%)	⬆️
lib/ex_webrtc/rtp/opus/payloader.ex	100.00% <100.00%> (+100.00%)	⬆️
lib/ex_webrtc/rtp/payloader.ex	100.00% <100.00%> (ø)
lib/ex_webrtc/rtp/vp8/payloader.ex	100.00% <ø> (ø)
lib/ex_webrtc/rtp/vp8/depayloader.ex	77.27% <0.00%> (ø)

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[sgfn]

@LVala I, too, thought that ex_doc would handle it, but alas

Without @spec in implementations:

With:

[LVala]

Removing the @doc will automatically add a doc with "Callback implementation for ". Indeed, not @spec in such a case.

Not sure which one is better, but having explicit spec seems more useful.

Edit: You also need to remove @impl true to generate the default doc, which is kinda yucky.

[mickel8]

I think that at the end of the day, we don't want to document functions from Opus/VP8 payloaders/depaylaoders. Instead, the whole documentation should be in the behaviour module or in the module that is responsible for dispatching or in both.

E.g.

d = ExWebRTC.RTP.Depayloader.new(ExWebRTC.RTP.Depayloader.VP8, some_options)
{frame, d} = ExWebRTC.RTP.Depayloader.depayload(d, packet)

In such case, we only need to document ExWebRTC.RTP.Depayloader.VP8 module. Its functions shouldn't appear in docs. But this is the final outcome.

[sgfn]

@mickel8 Could you please reiterate on how exactly do you suggest the docs should look like? Specifically, which parts should I get rid of?

[mickel8]

@sgfn please take a look at #154