[TextField] Partial support for HTML formating

Support <br>, <p> and <font>. Only one <font> tag is supported and
only in the beginning of the string.
Move unnecessary includes out of tags.h
[IOErrorEvent] Add (undocumented) constants
Validate namespace kind, fix an uninitialized pointer

nsNameAndKindImpl constructor now validates the kind argument.

http://en.calameo.com player defines the empty namespace with a
namespace kind 0, which is not documented as legal value.