Add documentation for pascaligo parser interface as .mli

src/passes/1-parser/pascaligo.mli

@@ -0,0 +1,21 @@
+(* This file provides an interface to the PascaLIGO parser. *)
+
+open Trace
+
+module Parser = Parser_pascaligo.Parser
+module AST = Parser_pascaligo.AST
+module ParserLog = Parser_pascaligo.ParserLog
+module LexToken = Parser_pascaligo.LexToken
+
+
+(** Open a PascaLIGO filename given by string and convert into an abstract syntax tree. *)
+val parse_file : string -> (AST.t result)
+
+(** Convert a given string into a PascaLIGO abstract syntax tree *)
+val parse_string : string -> AST.t result
+
+(** Parse a given string as a PascaLIGO expression and return an expression AST.
+
+This is intended to be used for interactive interpreters, or other scenarios 
+where you would want to parse a PascaLIGO expression outside of a contract. *)
+val parse_expression : string -> AST.expr result