Support incomplete XML input

[pocmo]

Needed for #5.

The XMLPullParser implementation only likes well-formed XML documents. E.g. when having multiple root nodes:

start tag not allowed in epilog but got T (position: END_TAG seen ...    android:text="padding"\n    android:background="#ff0000" />\n\n<T... @9:3) 
org.xmlpull.v1.XmlPullParserException: start tag not allowed in epilog but got T (position: END_TAG seen ...    android:text="padding"\n    android:background="#ff0000" />\n\n<T... @9:3)

But we also want to be able to recompose partial XML documents (e.g. see #5).

We could:

• Figure out if XMLPullParser supports a quirks mode that will continue parsing documents that are not strictly following the XML standard.
• Manually fix up the XML before parsing it (e.g. introducing a root node that we will skip when parsing).
• Use a different, more forgiving parser.
• Write a minimal parser implementation that parses tags / attributes and doesn't require strict XML documents.