Give docs a proper update

[jonhoo]

I've made a pass on pretty much all the docs, as well as the names of a few types, to try to clean up the externally-visible API. It'd be awesome if someone could give it all a read through and see that a) the structure of the API makes sense, b) I'm not saying anything totally false, and c) there aren't any gaping holes that we should fill immediately.

I have included any example code somewhat intentionally since I'm guessing the external APIs are likely to change a decent amount with #30.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@65587d8). Click here to learn what that means.
The diff coverage is 83.33%.

@@            Coverage Diff            @@
##             master      #61   +/-   ##
=========================================
  Coverage          ?   75.82%           
=========================================
  Files             ?       14           
  Lines             ?     1212           
  Branches          ?        0           
=========================================
  Hits              ?      919           
  Misses            ?      293           
  Partials          ?        0

Impacted Files	Coverage Δ
src/collapse/mod.rs	0% <ø> (ø)
src/flamegraph/color/palette_map.rs	0% <ø> (ø)
src/bin/collapse-perf.rs	0% <0%> (ø)
src/flamegraph/mod.rs	82.6% <100%> (ø)
src/flamegraph/attrs.rs	89.74% <100%> (ø)
tests/collapse-perf.rs	93.87% <100%> (ø)
src/collapse/perf.rs	81.5% <100%> (ø)
src/flamegraph/color/mod.rs	71.65% <80%> (ø)

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[jasonrhansen]

Looks really good to me! Other than the few typos I pointed out I have nothing to add.

[jonhoo]

@jasonrhansen great, thanks for the review! I'll leave this open for a bit longer in case @JordiChauzi also has a chance to take a look, otherwise I'll merge towards the end of today EST.

[JordiChauzi]

For different structures implementing Default, you precised the default value in the doc of the structure. Hopefully the value will not change overtime, but is it not redundant ?

[JordiChauzi]

The documentation is really clear and complete (minus the possible examples that we may add later).
Seems good to me.

[jonhoo]

I think it's useful to spell out the defaults in the docs since they're not otherwise visible anywhere beyond digging into the code. It's true that we'd have to make sure update the docs if the defaults change, but at the same time I think these defaults should also be relatively unlikely to change :)

[jonhoo]

Thanks for the review from both of you! I'll merge once CI passes!

[jonhoo]

@jasonrhansen I added some more docs following #60 in 3e706ea. Can you take a quick look?

[jasonrhansen]

Thanks for adding docs for differentials! I made "Flame Graph" the default for the title in Options. We should probably document that now.

[jonhoo]

@jasonrhansen done in 924421b