+ updating the data.tests to use Sequences
+ adding Execution.begin tracking
+ bringing back support for stripping shebangs
+ partial re-write of Execution and advance() to utilize the new parser
+ moving advance() tests to follow the method
+ basic parameter validation for Execution
+ typo in advance()
+ dunno why I thought _ would be available >,<
+ Sequence / Expression aren't arrays, but I *am* an idiot.
+ taking a response to advance() again
+ bad typo screwing up advance()
+ Sequence#at now dives down into expressions
+ rewriting most of the existing advancement tests!