Support gettext 3.0.0

Gettext 3.0.0 removes deprecated APIs.
See also: https://github.com/ruby-gettext/gettext/blob/master/doc/text/news.md#300-2013-08-31

API changes:

require "gettext/tools/poparser" ->
require "gettext/po_parser"

GetText::PoParser ->
GetText::POParser

require "gettext/runtime/mofile" ->
require "gettext/mo"

GetText::MoFile ->
GetText::MO
Support gettext 2.x again for Ruby 1.8

Gettext 3.0.0 drops Ruby 1.8 support but YARD doesn't drop Ruby 1.8
support yet. So YARD supports old gettext that supports Ruby 1.8
again.
Fix a typo in the README example.
Merge pull request #695 from zenhob/readme_example_typo

Fix a typo in the README example.
Fix possible XSS issue in frames anchor handling.

frames.html can parse the anchor in the address bar for a string
starting with "#!" that tells YARD which main frame to load. The
string parsed from the anchor was not sanitized, allowing for any
arbitrary HTML to be embedded into the page.

However, due to the HTML4 specification, HTML is not allowed inside
of a <frameset> tag, and any compliant browser should drop any such
markup from the DOM, negating a possible attack vector. It is still
possible to embed HTML inside of a <noframes> element, but very few
modern browsers will handle such a tag anyway. Given these factors,
the impact of such an XSS attack is very low.
Merge pull request #693 from kou/support-gettext-3.0.0

Support gettext 3.0.0
Bump version to 0.8.7.1
Support casted functions in RubyC method handler

References #697
Disallow absolute URLs in frames anchor handling
Bump to version 0.8.7.2
Ensure CONFIG_DIR exists before saving CONFIG_FILE

Fixes #700
Add support for dyna_symbol ripper node type

Fixes #701
Fix broken test in legacy mode
Fix Ruby 2.0 issue with highlighting of non-Ruby code blocks

Fixes #702
recognize all established AsciiDoc file extensions
Merge pull request #704 from mojavelinux/asciidoc-file-ext

recognize all established AsciiDoc file extensions
JavaScript bug fix for the default template.

When using the frames view in the default template,
it attempts to set the page title when you load a page in the
main frame.  If you are serving content from disk using file://,
some browsers, like Chrome, will raise an error. This stops
the rest of the JavaScript on the page from running.

This pull request adds a try-catch block around the window title
assignment statement.  In the case when this fails, the title simply
is not updated.
Updated css for Ruby syntax highlighting.

The label class name is used for styling the new symbolized hash
syntax from Ruby 1.9+.

    # "key" is a label and should be colored like a symbol.
    some_method(key: 'value')

Updated the color on label to match that of symbol.
Merge pull request #707 from trevorrowe/css-fix

Updated css for Ruby syntax highlighting.
Merge pull request #706 from trevorrowe/master

JavaScript bug fix for the default template.