feat: add inline union representation to schema parser

Closes: ipld/ipld#286

Prepare v0.19.0

fix: go mod 1.17 compat problems

feat(bindnode): support full uint64 range

add option to not parse beyond end of structure (ipld#435)

node/bindnode: allow binding cidlink.Link to links

We allowed the low-level go-cid.Cid as well as the generic ipld.Link,
but not the type that implements ipld.Link via a go-cid.Cid.
Allow all three to be consistent and nice towards the user.

The get/set code already handles the case correctly;
it's just verifyCompatibility that didn't account for it.

While here, make "kind mismatch" messages more verbose,
as otherwise they may be confusing to the user.

Fixes ipld#305.

Merge pull request ipld#308 from ipld/dagcbor-coerce-undef-to-null

dagcbor: coerce undef to null.

traversal: s/Walk/WalkLocal/

This function does not do link loading, even if those systems are
present in the traversal config; that's pretty significant, and the
function's name should say something about that.

Also: added documentation about the SkipMe behavior.

mark v0.14.0

Merge pull request ipld#257 from ipld/union-fixes-and-more-tests

schema,tests,gen/go: more tests, gen union fixes.