* chore: refactor to keep only the new parser and bytecode vm

* scanner: remove Token.value field

* scanner: remove scanner.kind field

* chore: move language specification in lang package

This avoid a cyclic dependency in scanner_test which can now use
the golang/GoSpec language specification for Go.

* clean code

* scanner: export scanner fields

Also parser now generate function calls, including externals.

* chore: fix lint issues

* parser: handle strings

* wip

* parser: implement support for 'if, else, else if' statements

Resolving labels in the compiler still in progress.

* parser: support if statements, improve compiler

* improve handling of functions

* improve support of local variables

* scanner: trim leading and trailing spaces

* fixes to make fibonacci work

* parser: improve README, fix function parameters parsing

The "Enter" instruction has been removed and the frame pointer is
now saved by the "Call" instruction.

The "Return" instruction now takes the number of function input
parameters as the second operand. It's used to return the output
values at the correct place in the caller frame, no matter the
number of input parameters.

The tests and the code generator have been updated accordingly.

* codegen: add a bytecode generator
* cleaning scanner, parser and vm1.