Node.js utils for parsing error stacks, applying source maps to error stacks, etc

• ParsedError class
  • can be constructed from an Error instance
  • stack lines are parsed into a data structure with filename/line/column info
  • can be manipulated and then converted back into a normal Error
  • has a stack property getter which makes a V8-style stack string from the parsed stack frames
• applySourceMapsToParsedError function
  • updates the line/column numbers on the stack frames of a ParsedError by using source maps
  • returns a new ParsedError
• applySourceMapsToStackFrame function
  • same as above but for a single StackFrame
• getStackFrame function
  • given a stack offset number, gets a StackFrame instance from the current callstack.
  • offset of 0 gives the call to getStackFrame.
  • can be used to obtain the file name and (sometimes) function name of the currently-executing file, or one of its callers.
• isError function
  • type predicate function
  • returns true for objects with shape { name: string, message: string } when name ends with "Error"