Update library to Contributors library standards

[maxdeviant]

This PR updates purescript-matryoshka to adhere to the Contributors library guidelines.

This is part of the purescript-contrib/governance#13 effort.

[maxdeviant]

Verified that the build works and the "tests" run:

λ spago build
[info] Installation complete.
[info] Build succeeded.

λ spago test
[info] Installation complete.
[info] Build succeeded.
expr example
24
list example
24
4 : 3 : 2 : 1 : Nil
720
[info] Tests succeeded.

Once this PR gets merged I'll add issues for the following outstanding items:

• Adding a "quick start" guide
• Adding real tests (currently they're just runnable examples)
• Adding module documentation

[maxdeviant]

Once this PR gets merged I'll add issues for the following outstanding items:

• Adding a "quick start" guide
• Adding real tests (currently they're just runnable examples)
• Adding module documentation

I went ahead and created these issues now, since I forgot to do it once purescript-contrib/purescript-arraybuffer-types#16 was merged 🤦‍♂️

[thomashoneyman]

Couple of minor comments, but otherwise 👍