Allow blockprocessor.run to return True or False.

This allows the run method to determine if a block is or is not a match in the
midst of parsing outside of the test method. The goal is to eliminate the
often redundant test method in the future. In the interim, it remains and
if the run method returns None, the existing behavior is maintained. Returning
None may generate a DepreciationWarning later. Note that test must still return
True to even get to the run method.
Remove `<ins>` and `<del>` from html block element list

They are span elements. `<del>` is explicitly mentioned as such in the [markdown syntax document](http://daringfireball.net/projects/markdown/syntax)
Merge pull request #93 from fin/master

Remove `<del>` and `<ins>` from block-level elements list
tests for 9852c2263ef7775d2a508a9c1721148cbf3ae258
Merge pull request #94 from fin/master

added a test for the previous pull request
Fixed #87

Elements should be inserted in the tree regardless of enable_attributes
Add test for 5236a9838c580a17c3299efb97d9f41ce2a1efab
Merge pull request #95 from cataliniacob/master

Attempted fix for issue 87
Fixed #82. 'enable_attributes' honors 'safe_mode'.

Note that you can still explicitly set 'enable_attributes' and that
value will be honored regardless of 'safe_mode'. However if 'safe_mode'
is on and 'enable_attributes' is not explicitly set, then
'enable_attributes' defaults to False.
Updated docs to reflect fix in #82.
Added release notes for v2.2.0.
Updated version to 2.2.0.alpha.
Merge branch 'master' of github.com:waylan/Python-Markdown
Fixed Issue #98. The language designator must start at the beginging of the first line of a code block for codehilite to recognize it.
Fix #99. Account for empty header IDs when ensuring uniqueness.
Fixed #105. Non-existant extensions fail with a warning only.
Fixed #109. The attr_list extension can now be loaded either before or after the headerid extension.
Fixed #110. Documented the 'fenced_code' extension's support for the 'codehilite' extension.
Fixed #106. Replaced all references to freewisdom.org (except for Yuri's homepage).
Added .md to README.md etc in MANIFEST.in.