Added Table#sort_cursor
Use Symbol for method name on Ruby 1.9
Extract dynamic methods collect code
Don't follow non table columns
Add a missing space
Table#sort returns Groonga::Array instead of Array

CAUTION: This is backward incompatible change. You need to use
record.value to get the original record. The following code shows
how to use old style:

  result_since_2_1_0 = table.sort(["sort_key"])
  result_before_2_1_0 = result_since_2_1_0.collect do |record|
    record.value
  end

GitHub: close #8

Suggested by Genki Takiuchi. Thanks!!!
Follow backward incompatible API change of Groonga::Table#sort
doc: unify the document about DoubleArrayTrie#open_prefix_cursor with @!macro

refs #1519
doc: use @!macro in the document about Schema.create_table (w.i.p)

refs #1519

TODO:
* Move the document about Schema#create_table with
  :type=>:double_array_tie to Schema.create_table.
* Use the same document for Schema#create_table by @!macro.
doc: move the document about create_table() with dat from Instance to Class

refs #1519

This document is displayed in the reference of instance methods too,
by @!macro.
doc: use @!macro for each option for Schema#create_table

refs #1519

The original documents with @!macro are written in Schema.create_table.
Use Packnga 0.9.4 later
Follow packnga's document about DocumentTask

Symbol -> String
Don't use abbreviation name

t -> task
doc: create PO file for Japanese with packnga 0.9.7

TODO: translate and resolve fuzzy after 2.1.0 entry is added to news.textile
doc: add 2.1.0 entry
Add missing textile files to gemspec
Add missing require
Fix the bug that the first line of AUTHORS is added to author and email
doc: update 2.1.0 entry for YARD