Add some new links between syntax and highlight

Some new links have been added or changed in order to beautify the Ruby
syntax.

after/syntax/ruby.vim

@@ -0,0 +1,11 @@
+" Maintainer: Ludovic Koenig <ludovic.koenig@gmail.com>
+" Version: 0.6.0
+" Since: 0.6.0
+" License: MIT
+"
+" Ruby Syntax {{{
+
+syntax keyword rubyOdysseyNil nil
+
+" }}}
+" vim: foldmethod=marker

colors/odyssey.vim

@@ -320,16 +320,24 @@ call s:l(                'rubyDefine',  'Statement')
 call s:l(               'rubyInclude',    'Statement')
 call s:h(      'rubyInstanceVariable',   'background', 'warning', 'italic')
 call s:l('rubyInterpolationDelimiter',     'Function')
-call s:l(       'rubyStringDelimiter',   'Function')
+call s:l(       'rubyStringDelimiter',       'Normal')
 call s:l(                'rubyAccess',    'Statement')
 call s:l(             'rubyAttribute',    'Statement')
 call s:l(        'rubyPseudoVariable',      'Special')
+call s:l(                'rubySymbol', 'rubyConstant')
+call s:h(        'rubyBlockParameter',   'background', 'procedure', 'italic')
+call s:l(            'rubyOdysseyNil',       'Normal')
+call s:l(               'rubyBoolean',       'Normal')
+call s:l(                 'rubyFloat',       'Normal')
+call s:l(               'rubyInteger',       'Normal')
 
 " }}}
 " Rust Highlights {{{
+
 call s:l(       'rustLifetime', 'Constant')
 call s:l(   'rustQuestionMark', 'Operator')
 call s:l('rustOdysseyFunction', 'Function')
 call s:l(    'rustOdysseyType',     'Type')
+
 " }}}
 " vim: foldmethod=marker