Ignore .DS_Store and swap files
Error handling changes.

- Install error handlers before functions using them, so they're installed on the relevant thread.
- Build error instance in error handler, rather than relying on pointer remaining valid.
- Extract libxml2 error when parsing an XML document, attach to existing error as an underlying error.
Enable "Suspicious Implicit Conversions" warning and fix occurances
Enable "Hidden Local Variable" warning and fix occurance
Added a project to build a static library.
Copy the header files to ${BUILT_PRODUCT_DIR}/include/${PRODUCT_NAME}.

This is a good place for dependent projects to find them.
Implement DDXMLNode nodesForXPath:namespaceMappings:error.

This allows the caller to pass in an NSDictionary specifying the mapping
from namespace prefix to namespace URL.  Namespace prefixes specified in
the given XPath will then be resolved against that mapping.

This allows callers to find nodes using default namespaces, e.g.
<element xmlns='<schema URL>'>...</element>.  The caller must specify
prefix=<schema URL> in namespaceMappings, and then can use prefix:element
in the XPath.

If namespaceMappings is nil, then the existing behavior is used
(parsing the namespaces from the document node).  This works in the
situation where the namespaces are all named explicitly, and all on the
root node, but not in general.

This addresses upstream issue #19, the second half of issue #20.
Merge branch 'nodesforxpath-namespacemappings'
Merge remote-tracking branch 'noa--/gitignore'
Use xmlDocGetRootElement when setting up namespaces.

The existing code uses doc->children, which is wrong in the case that the
document has a doctype or PI nodes at the start.

This fix is originally from upstream issue #20, by kgrigsby59.

This changeset re-applies the fix on top of the
nodesforxpath-namespacemappings branch (the two changes are in the same
area of code).
Merge branch 'nodesforxpath-docroot-fix'
Merge remote-tracking branch 'ThomasHaukAbsoluteSoftware/4.1.1-with-local-changes'
Merge remote-tracking branch 'tewha/error'
Merge branch 'ns-declarations-enabled'
Remove unused variable.
Merge branch 'error-unused-var-fix'