conditionals.
Enabled in parser a type annotation on lambda parameter, and
lifted the existing type annotation in patterns to become that
type annotation.
More precisely,
* I commented out the operator "@" on lists in Ligodity (it can
be implemented as a function, as a workaround).
* I removed the parallel "let" construct (hence the "and" keyword).
* I renamed the type "field_assignment" into "field_assign", in
order to match Pascaligo AST.
* The reading of the command-line options is now done by
calling the function [EvalOpt.read], instead of an ugly
side-effect when loading the binary of the module. Options
are now found in a record of type [EvalOpt.options].
* I added support in the Ligodity lexer for #include CPP
directives.
