fix(js): keep finally blocks reachable after return or throw (#172)

[DaisukeYoda]

Fixes #172.

A finally block runs however its try or catch ends. The CFG builder connected the try and catch to the finally block only when they completed normally, so a finally after a return, throw, break or continue was reported as unreachable_branch.

The builder now adds an exception edge into the finally block from the try block, or from the catch block when there is one. That edge stands for every abrupt exit, so the finally block is reachable whenever the try is. The finally block connects to the code after the try only when the end of the try or catch is reachable from the start of the try and does not end with a jump, so after() in try { return } finally { ... } after() is still reported. Exception edges do not count toward cyclomatic complexity, so complexity does not change.