v0.16.0

This release was mostly about introspection and interoperability.

• Implement (builtins), (specials), and (stdlib).
• Updated (join) to take an optional second parameter.
  • This is inserted between the list values as part of the flattening.
• Added (find), (flatten), and (occurrences) to stdlib/stdlib/lists.lisp.
• Allow functions to have default values for arguments.
  • Introduced in #131, after being reported in #130.
  • (inc) and (dec) have been updated to use this support.
• Implemented (body) and (source) to return the body/source of a lisp primitive.
  • Implemented in #132, after inspiration from l1 in #115.
• Added (exit) and (forever) as special forms.
  • Implemented in #135, after being reported in #133.
• Added ($ "ls -l|wc -l") as another special.
  • This allows running shell commands and returns the output as either a string, or a list.
  • Implemented in #136, after being reported in #134.