[Notice] Absolute v2: Start from scratch

[romandev]

After long discussion, we decided to restart from scratch as v2. So, we changed absolute_2.0 working branch to master branch and rename existing master branch with absolute_v1 branch and froze it. Please see the related change: https://github.com/lunchclass/absolute/commit/178221c65481410c9d6c3277ad17f7c91563366d

So, TypeScript migration work we were doing in v1 should keep going on the work in new master branch by cherry-picking patches or migrating codes from absolute_v1 branch.

Also, it's better to use absolute_v2 label for newly registered issues, until we close all legacy issues.