Replace gopkg.in/check.v1 with the standard testing library

Signed-off-by: Davanum Srinivas <[email protected]>

Simplify simple key tracking

Signed-off-by: Tim Ramlot <[email protected]>

Minimal fix for 2 Makefile bugs

'make test' was not working from a clean state.
'make clean' was not removing the go-yaml CLI.

Retract v2 tags that cannot be installed

Change error message about decoding into Go map

YAML allows sequences and mappings as a key for a mapping.
Go does not support slices or maps as a map key; and the default
decoder returns an error "yaml: invalid map key %#v". but i feel
that this error message is misleading and may cause the user to
think that it's an error in the document.

i updated the error message to be indicate this situation and ask
the user to try `yaml.Node`

Fix errors from alias/anchor with non alnum name

closes #44

Downgrade the go version number in go.mod

[v3] Fix the URL in the package documentation

[v3] Formalize new package name

go.yaml.in/yaml/v3

[v2] Fix the URL in the package documentation