minor fixes
- add main.$currentThread
- fix constant values
- rename null -> nil
- README++
Merge pull request #65 from mohayonao/minor-fixes

minor fixes
- improve SCRoutine
- reimplement sc.lang.bytecode
- build v0.0.51
Merge pull request #66 from mohayonao/implements-routine

- improve SCRoutine
Merge branch 'master' into gh-pages
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