Use spago instead of pulp and bower

[connorads]

Summary

This PR updates the PureScript docs and exercises to use spago.
Fixes #119

spago is now preferred over bower on PureScript website and getting started guide.

Todo

• Update INSTALLATION.md and TESTS.md
• Replace exercises bower.json with packages.dhall and spago.dhall
• Update .gitignore
• Fix build break related to check-bower.sh
• Update other scripts
• Update README.md
• Update .travis.yml

More info

Used spago init to migrate each exercise and then deleted the respective bower.json.

spago init   
[info] Initializing a sample project or migrating an existing one..
[info] Found a "bower.json" file, migrating to a new Spago config..
[info] All Bower dependencies are in the set! ?
[info] You can now safely delete your "bower.json"
[info] Updating package-set tag to "psc-0.13.8-20201223"    
Fetching the new one and generating hashes.. (this might take some time)
[info] Generating new hashes for the package set file so it will be cached.. (this might take some time)
[info] Found existing directory "src", skipping copy of sample sources 
[info] Found existing directory "test", skipping copy of sample sources
[info] Set up a local Spago project.
[info] Try running `spago build`

Then used spago test to install packages and run tests.
All the packages seemed to install and then the tests seem to fail as expected.

spago test
Compiling PascalsTriangle
Error found:
in module PascalsTriangle
at src\PascalsTriangle.purs:1:25 - 1:29 (line 1, column 25 - line 1, column 29)

  Cannot export unknown value rows


See https://github.com/purescript/documentation/blob/master/errors/UnknownExport.md for more information,
or to contribute content related to this error.


[error] Failed to build.

[guygastineau]

@connorads Do you want some extra fingers on this PR?

[connorads]

Yes, would love them!

[guygastineau]

Alright, I will try to find some time. purescript did manage to piss me off a bit over the last hour lol (I just want it to be Haskell in the browser, and it is NOT that). Still, I guess it is the closest I can get.

[emiel]

I'd also like to see this moving along and can spend some time on it. I'm curious who is able to merge these PRs... @aimorris ?

[aimorris]

I can merge the PR once it's complete. I might be able to help out over the next week, or I might not.

[ErikSchierboom]

@emiel Is this superseded by #189 and can it be closed?

[emiel]

@ErikSchierboom : As far as I'm concerned everything in this PR is covered by the changes now in main (#189). There are some remaining "cleanup" items to take care of (updating the documentation, removing some leftovers, etc). Thanks to @connorads for the initial push!

• Remove bower leftovers (post spago migration) #202
• Update documentation after introducing spago #193
• Exercise dependencies #186