Wrote Toy_Lexer, Toy_Parser API

c-api/toy_lexer_h.md

@@ -0,0 +1,10 @@
+# toy_lexer.h
+
+This header defines the structure `Toy_Lexer`, which can be bound to a piece of source code, and used to tokenize it within a parser.
+
+## Defined Functions
+
+### void Toy_initLexer(Toy_Lexer* lexer, const char* source)
+
+This function initializes a lexer, binding it to the `source` parameter; the lexer is now ready to be passed to the parser.
+