Add Unit Tests (#5)

* Add unit tests.

Signed-off-by: txaty <xtianae@connect.ust.hk>

* Add unit tests.

Signed-off-by: txaty <xtianae@connect.ust.hk>

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Signed-off-by: txaty <xtianae@connect.ust.hk>

Merge pull request #3 from txaty/generics

Refactor, update License.

Merge pull request #2 from txaty/generics

Add async methods and invalid number handling

Update README.md

Submit and Map methods.

Submit and SubmitBatch