Officially support Windows

On Windows, MRI Ruby uses the `FindFirstFileW` et. al. kind of functions with
wide character paths and constantly converts from multi-byte to wide character
encoding back and forth when calling any methods on `File` or `Dir`.

This means that when using `Encoding::ASCII_8BIT` for reading directory entries,
that this does not round trip properly, if a file name contains unicode
characters. That is because Ruby assumes the path string is encoded in Windows
Codepage 1252[1].

* skip symlink test if files were checked out from git as textual symlinks on
  Windows
* use UTF-8 encoding on Windows, since this properly round-trips between
  multi-byte and wide character encoding
* travis: windows job no longer is allowed to fail

[1]: https://github.com/ruby/ruby/blob/946cd6c5348d7dd12ecc41e79c3ca9803d2ca7f0/win32/file.c#L131-L134

.travis.yml

@@ -21,7 +21,6 @@ jobs:
 
   allow_failures:
     - rvm: truffleruby-head
-    - os: windows
 
   include:
     - os: osx

lib/colorls/core.rb

@@ -1,6 +1,13 @@
 # frozen_string_literal: true
 
 module ColorLS
+  # on Windows (were the special 'nul' device exists) we need to use UTF-8
+  @file_encoding = File.exist?('nul') ? Encoding::UTF_8 : Encoding::ASCII_8BIT
+
+  def self.file_encoding
+    @file_encoding
+  end
+
   class Core
     def initialize(input, all: false, report: false, sort: false, show: false,
       mode: nil, git_status: false, almost_all: false, colors: [], group: nil,
@@ -79,7 +86,7 @@ def init_contents(path)
       info = FileInfo.new(path, link_info: @long)
 
       if info.directory?
-        @contents = Dir.entries(path, encoding: Encoding::ASCII_8BIT)
+        @contents = Dir.entries(path, encoding: ColorLS.file_encoding)
 
         filter_hidden_contents
 
@@ -283,14 +290,18 @@ def symlink_info(content)
       end
     end
 
+    def out_encode(str)
+      str.encode(Encoding.default_external, undef: :replace, replace: '')
+    end
+
     def fetch_string(path, content, key, color, increment)
       @count[increment] += 1
       value = increment == :folders ? @folders[key] : @files[key]
       logo  = value.gsub(/\\u[\da-f]{4}/i) { |m| [m[-4..-1].to_i(16)].pack('U') }
       name = content.show
       name = make_link(path, name) if @hyperlink
       name += content.directory? ? '/' : ' '
-      entry = "#{logo.encode(Encoding.default_external, undef: :replace, replace: '')}  #{name}"
+      entry = "#{out_encode(logo)}  #{out_encode(name)}"
 
       "#{long_info(content)} #{git_info(content)} #{entry.colorize(color)}#{symlink_info(content)}"
     end

spec/color_ls/flags_spec.rb

@@ -152,7 +152,7 @@
   end
 
   context 'with --sort=time' do
-    entries = Dir.entries(FIXTURES).grep(/^[^.]/).shuffle.freeze
+    entries = Dir.entries(FIXTURES, encoding: Encoding::UTF_8).grep(/^[^.]/).shuffle.freeze
     mtime = Time.new(2017, 11, 7, 2, 2, 2).freeze
 
     files = entries.each_with_index do |e, i|
@@ -276,7 +276,13 @@
   context 'symlinked directory with trailing separator' do
     let(:args) { ['-x', File.join(FIXTURES, 'symlinks', 'Supportlink', File::SEPARATOR)] }
 
-    it { expect { subject }.to output(/yaml_sort_checker.rb/).to_stdout }
+    it 'should show the file in the linked directory' do
+      if File.symlink? File.join(FIXTURES, 'symlinks', 'Supportlink')
+        expect { subject }.to output(/yaml_sort_checker.rb/).to_stdout
+      else
+        skip "symlinks not supported"
+      end
+    end
   end
 
   context 'when passing invalid flags' do