convert english README from rdoc to markdown

Manifest.txt

@@ -4,7 +4,7 @@ DOCUMENTATION.en.rdoc
 DOCUMENTATION.ja.rdoc
 Manifest.txt
 README.ja
-README.rdoc
+README.md
 Rakefile
 bin/rex
 lib/rexical.rb

README.md

@@ -0,0 +1,57 @@
+# Rexical
+
+* http://github.com/sparklemotion/rexical
+
+## DESCRIPTION
+
+Rexical is a lexical scanner generator that is used with Racc to generate Ruby programs. Rexical is
+written in Ruby.
+
+
+## SYNOPSIS
+
+Several examples of Rexical grammar files are provided in the sample directory.
+
+Here is an example of a lexical definition:
+
+    class Sample
+    macro
+      BLANK         [\ \t]+
+    rule
+      {BLANK}       # no action
+      \d+           { [:digit, text.to_i] }
+      \w+           { [:word, text] }
+      \n
+      .             { [text, text] }
+    end
+
+Here are examples of the command line usage:
+
+    $ rex  sample1.rex  --stub
+    $ ruby sample1.rex.rb  sample1.c
+
+    $ rex  sample2.rex  --stub
+    $ ruby sample2.rex.rb  sample2.bas
+
+    $ racc calc3.racc
+    $ rex  calc3.rex
+    $ ruby calc3.tab.rb
+
+The description files for lexical analysis in the sample directory are the files ending with the
+.rex extension.
+
+## REQUIREMENTS
+
+*  ruby version 1.8.x or later.
+
+## INSTALL
+
+* sudo gem install rexical
+
+## LICENSE
+
+Rexical is distributed under the terms of the GNU Lesser General Public License version 2. Note that
+you do NOT need to follow LGPL for your own parser (Rexical outputs). You can provide those files
+under any licenses you want.
+
+See COPYING for more details.

rexical.gemspec

@@ -12,8 +12,8 @@ Gem::Specification.new do |s|
 
   s.executables = ["rex"]
 
-  s.rdoc_options = ["--main", "README.rdoc"]
-  s.extra_rdoc_files = ["CHANGELOG.md", "DOCUMENTATION.en.rdoc", "DOCUMENTATION.ja.rdoc", "README.rdoc"]
+  s.rdoc_options = ["--main", "README.md"]
+  s.extra_rdoc_files = ["CHANGELOG.md", "DOCUMENTATION.en.rdoc", "DOCUMENTATION.ja.rdoc", "README.md"]
 
   s.files = File.read("Manifest.txt").split("\n")