Make the FLOAT_LITERAL rule mention keywords as well as identifiers

Author: mattheww

src/tokens.md

@@ -444,7 +444,7 @@ let horse = example.0b10;  // ERROR no field named `0b10`
 > **<sup>Lexer</sup>**\
 > FLOAT_LITERAL :\
 > &nbsp;&nbsp; &nbsp;&nbsp; DEC_LITERAL `.`
->   _(not immediately followed by `.`, `_` or an [identifier]_)\
+>   _(not immediately followed by `.`, `_` or an [identifier] or [keyword][keywords]_)\
 > &nbsp;&nbsp; | DEC_LITERAL FLOAT_EXPONENT\
 > &nbsp;&nbsp; | DEC_LITERAL `.` DEC_LITERAL FLOAT_EXPONENT<sup>?</sup>\
 > &nbsp;&nbsp; | DEC_LITERAL (`.` DEC_LITERAL)<sup>?</sup>