Improve handling of numbers in Kotlin lexer (#1509)

This commit improves the handling of numbers in the Kotlin lexer.
Specifically, it:

1. adds support for underscore separators;
2. adds support for binary literals;
3. removes invalid support for the lowercase "l" suffix; and
4. adds support for unsigned literals.

lib/rouge/lexers/kotlin.rb

@@ -67,13 +67,20 @@ class Kotlin < RegexLexer
         rule %r'\n', Text
         rule %r'::|!!|\?[:.]', Operator
         rule %r"(\.\.)", Operator
+        # Number literals
+        decDigits = %r"([0-9][0-9_]*[0-9])|[0-9]"
+        exponent = %r"[eE][+-]?(#{decDigits})"
+        double = %r"((#{decDigits})?\.#{decDigits}(#{exponent})?)|(#{decDigits}#{exponent})"
+        rule %r"(#{double}[fF]?)|(#{decDigits}[fF])", Num::Float
+        rule %r"0[bB]([01][01_]*[01]|[01])[uU]?L?", Num::Bin
+        rule %r"0[xX]([0-9a-fA-F][0-9a-fA-F_]*[0-9a-fA-F]|[0-9a-fA-F])[uU]?L?", Num::Hex
+        rule %r"(([1-9][0-9_]*[0-9])|[0-9])[uU]?L?", Num::Integer
         rule %r'[~!%^&*()+=|\[\]:;,.<>/?-]', Punctuation
         rule %r'[{}]', Punctuation
         rule %r'@"(""|[^"])*"'m, Str
         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'(@#{class_name})', Name::Decorator
         rule %r'(#{class_name})(<)' do
           groups Name::Class, Punctuation

spec/visual/samples/kotlin

@@ -182,4 +182,10 @@ loop@ for (i in 1..100) {
     }
 }
 
+val ints = listOf(1, 4_20, 100L, 123_345_678U)
+val bins = listOf(0b1, 0B0, 0b10_10_01, 0b10U, 0b10uL)
+val hexes = listOf(0xFF, 0Xa, 0x10L, 0X0UL)
+val exponents = listOf(1e10, -1E10F, 1.5e10, 1e-10)
+val doublesAndFloats = listOf(3.14, .99, 22f, 1_000.000_1, 19.95F)
+
 // comment at EOF (#797)