Release finschia-kt v0.2.1

[zemyblue]

Release v0.2.1

Changed

• #6 Rename package 'ln.v2' -> 'sdk'
• (ci) #11 Add ci/cd to publish to maven

Build, CI

• (build) #4 Add gradle updateSubmodule task and checkoutSubModule task to run git submodule update --init --remote with specific version before build task

[CLAassistant]

All committers have signed the CLA.

[jaeseung-bae]

In READMD.md. We can remove L14, L17~L32.
git submodule operation is done by gradle.