Refactor/ Make module become zero-dependencies (#7)

- Remove these dependencies:

    - `github.com/pkg/errors`
    - `github.com/stretchr/testify`

- Update unit tests and err messages the the module returns
- Update codecov config

Merge pull request #4 from sonh/dependent/upgrade-go-version

Bump go version from 1.15 to 1.19

Merge pull request #3 from sonh/fix/encoding-empty-slice

Fix encoding for empty slice that causes panic

Merge pull request #1 from agtabesh/fix/nested-struct

Fix incorrect logic in encoding nested struct index

Add codecov.yml

Support for map

Support for interface type

Fix tag parse error for embed struct

Add int format for bool type

Add codecov badge