Syntax Changes, Explicit References and JSON/smgpack serialization.

0.3.0 (2019-09-13)

• Incompatible Change: Removed :wref and :ref definition labels in favor of
  proper $&&, $& and $* reference handling. Added wl:weaken and wl:set_ref and
  .*x = ... syntax for even more reference handling.
• Incompatible Change: Replaced [] with () parenthesis. This means function calls
  are now having the [] brackets as argument list delimiters and
  regular arithmetics and expression grouping/delimiting is done with the more
  traditional () parenthesis. This is hopefully the last big incompatible syntax change
  before the 1.0 release.
• Feature: ser:json got a non-pretty print argument.
• Doc: Documented ser:json and deser:json, with additional examples.
• Feature: ser:msgpack and deser:msgpack added.
• Feature: Implemented wl:eval for evaluating wlambda code from inside
  wlambda code, so you can evaluate code while you are evaluating code.
• Feature: Thread communication helpers implemented for connecting
  WLambda EvalContext instances accross threads and providing easy
  cross thread messaging and RPC.
• Feature: Custom userdata can be implemented using the VValUserData trait.
• Feature: Added more bytes related functions and call properties.
  bytes:to_vec, bytes:from_vec, bytes:to_hex, bytes:from_hex,
  str:to_utf8, str:from_utf8, str:from_utf8_lossy.
• Feature: Added len function to get the length of vectors and other
  sequential data structures. str:len returns the length in unicode characters
  now.
• Bugfix: Weak upvalue references were not properly handled and directly returned
  by variable accesses.

0.2.2 (2019-09-01)

• - and + are not parsed as operator if a digit follows.
  fun :bar -2 2 was parsed as operator call for -.
  Sometime in the future we should change to a proper tokenizer.
• Bugfix: Assigning to a local variable cleared it's :ref state.
• Feature: Added optional serde/serde_json implementation and prelude
  function ser:json and deser:json.

0.2.1 (2019-07-18)

• Removed unprefixed destructuring syntax for a more consistent syntax.
• Assignments and definitions no longer return the stored value because
  it mixes badly with $error values.