Improve parsing of numbers in Kotlin lexer

- Adds support for underscore separator.
- Add support for binary literals.
- Removes invalid support for lowercase "l" suffix.
- Adds support for unsigned literals.

lib/rouge/lexers/kotlin.rb

@@ -73,7 +73,7 @@ class Kotlin < RegexLexer
         rule %r'""".*?"""'m, Str
         rule %r'"(\\\\|\\"|[^"\n])*["\n]'m, Str
         rule %r"'\\.'|'[^\\]'", Str::Char
-        rule %r"[0-9](\.[0-9]+)?([eE][+-][0-9]+)?[flFL]?|0[xX][0-9a-fA-F]+[Ll]?", Num
+        rule %r"(([0-9]|_)+(\.([0-9]|_)*)?[eE][+-]?([0-9]|_)*)[fF]?|((0[xX][0-9a-fA-F_]*[0-9a-fA-F])|(0[bB][01_]*[01])|([0-9]([0-9]|_)*)[uU]?L?)", Num
         rule %r'(@#{class_name})', Name::Decorator
         rule %r'(#{class_name})(<)' do
           groups Name::Class, Punctuation

spec/visual/samples/kotlin

@@ -182,4 +182,12 @@ loop@ for (i in 1..100) {
     }
 }
 
+val oneMillion = 1_000_000
+val creditCardNumber = 1234_5678_9012_3456L
+val socialSecurityNumber = 999_99_9999L
+val hexBytes = 0xFF_EC_DE_5E
+val bytes = 0b11010010_01101001_10010100_10010010
+val exponents = listOf(1e10, -1E10F, 1.5e10, 1e-10)
+val unsigned = 420U
+
 // comment at EOF (#797)