Add customize option for code wrapper, escape spesial chars and lang tag

[velp]

These options allow you to use the module for generating html with a specific syntax of code block. For example, the generation of the page to confluence:

>>> import markdown
>>> txt = """some text
... ```bash
... some code
... ```
... Title:
... 
... 1. first
... 2. second
... """
>>> ext_conf = {'fenced_code': {
...                             'escape': False,
...                             'code_wrap': '<ac:structured-macro ac:name="code">%s<ac:plain-text-body><![CDATA[%s]]></ac:plain-text-body></ac:structured-macro>',
...                             'lang_tag': '<ac:parameter ac:name="language">%s</ac:parameter>'
...                             }
...             }
>>> markdown.markdown(txt, extensions=['fenced_code'], enable_attributes=True, extension_configs=ext_conf)
u'<p>some text</p>\n<p><ac:structured-macro ac:name="code"><ac:parameter ac:name="language">bash</ac:parameter><ac:plain-text-body><![CDATA[some code\n]]></ac:plain-text-body></ac:structured-macro></p>\n<p>Title:</p>\n<ol>\n<li>first</li>\n<li>second</li>\n</ol>'
>>>

The Atlassian confluence used its formatting macros.

The result page:

[waylan]

I don't see any reason why a "confluence" extension couldn't exist as a separate extension. Personally, I have no use for this and have no desire to maintain it. Of course, if you desire to release a third-party extension, feel free to list it on the wiki