Configure Typedoc for @truffle/codec

[gnidan]

See preview here

This PR introduces a Typedoc for the codec, as well as organizes the code a bit to make docs organization a bit easier/cleaner. Opening this as a draft, since, at least, the commits need some rebasing... or at most, we may want to continue to organize the code more before merging this.

Notes

Typedoc configuration

• Docs are built with a forked package @gnd/typedoc right now... I forked off TypeStrong/typedoc@09a37f2 and included support export-declaration TypeStrong/typedoc#1079. Not sure if 1079 is necessary, but support for TS v3.6.x is, and that hasn't been released to NPM yet.
• I've included the regular typedoc dependency, as this is needed by typedoc plugins. This seems to work fine.
• I added a new "main" lib/index-typedoc.ts. This is the file that Typedoc loads to find what to document. Everything exported by that file, directly or indirectly, is considered "internal", namely... that's the public API.

Code stuff

• I got rid of the namespaces for Types, Values, and Errors. Instead, the respective modules have been imported with name in lib/format/index.ts, and the rest of the codebase now favors importing directly from lib/format.
• I moved a bunch of the error classes into the places where they seem to live.
• I grouped the decoder classes into lib/interface/decoders and did a similar named re-export called Decoders.
• I got rid of the ^Truffle prefix for those class names.
• I haven't done anything with lib/types/decoding or lib/types/interface yet, but I think we ought to.
• Basically, I tried to get everything organized at the public interface level, grouped into clear names. So far there's Format, Decoders, and Errors, but it'd be nice to think about how we can organize the other parts also. Note, this excludes forProject and friends... I think those should be top-level.
• Namespaces are terrible; we should just use modules.

Considerations for work to do

• It might be worth eliminating lib/index-typedoc.ts and just using lib/index.ts. We can use the @hidden tag to hide things manually.
• Is there no public API for encoding yet? Will that make it into the Decoders classes? Should we rename those to account for both capabilities?
• What's the point lib/interface? Can we make it more meaningful (like, make that the interface for real), or should we get rid of it?
• There's probably other stuff I'm forgetting now. Let's sync up about code structure!

Other notes

• You might want to turn off whitespace changes when viewing this PR, since the elimination of a namespace means indentation changes.
• Harry, tell your editor to delete trailing whitespace and to add new lines to the end of files 😈

[coveralls]

Coverage remained the same at 70.422% when pulling feaae80 on codec-docs into b9b4a0e on next.

[haltman-at]

Basically just rubber-stamping this, we can review the rearrangements when coalescements is PR'd.