v2.6.3

Cthulhu v2.6.3

Diff since v2.6.2

Closed issues:

• UndefRefError when optimization is enabled (#277)

Merged pull requests:

• rm dead logic (#300) (@aviatesk)
• fix #277, handle a callsite whose source is discarded due to recursion (#301) (@aviatesk)
• make logging more consistent (#302) (@aviatesk)