* iota

* iota-example

* clean

Without validation, multiple definitions of multiple enums in the same file
would be mixed, as well as comments with `json:"..."` on `val` or `const`
statments.

Fixes #24

Detect type when explicitly available. Infer when implicity known via a
composite type (of the first enum value). Punt with warning when neither
is possible (i.e. when type not explicitly stated, and value is literal
or expression). Exit with error when type canont be matched.

Fixes #24

The `const`/`var` block is expected to be found in the line immediately
subsequent to that of the `#go:generate`. Use the latter to precisely
locate the relevant block. This significantly simplified the solution
to the original issue.

Fixes #24

Add the env variable GOLINE=..., needed to vet the relevant const/var block.

Add a test case with multiple enum definition in the same file.

Add a test case to expect an error when the const/var block is not found in
the line following the `//go:generate ...` comment.

Remove unneeded output files from internal/testdata (uneeded copies of the
same files in internal/testdata/exp).

Signed-off-by: Nikolay Dubina <nikolay.dubina.pub@gmail.com>