Add Lexer API

Lexer-API.md

@@ -0,0 +1,27 @@
+The `interpret` helper object exposes the Lexing and Parsing API.
+
+## Methods
+
+### `interpret.first(input: str)`
+
+Peeks the first token in the input string.
+
+Returns: `Token`
+
+### `interpret.input(prompt: str)`
+
+An `input(prompt: str)` wrapper that tokenizes the user input.
+
+Returns: `TokenSet`
+
+### `interpret.parse_roll(input: str)`
+
+Parses `input` using the default roll expression parser.
+
+Returns: `int`
+
+### `interpret.tokenize(input: str)`:
+
+Tokenizes a string.
+
+Returns: `TokenSet`