Add explanations of 3 Woodstox-specific config properties in Wiki

[cowtowncoder]

(from #140)

StAX and StAX2 properties have remained stable over the years. But wrt the Woodstox-specific (input) properties, the following should be added to the Wiki:

• P_ALLOW_SURROGATE_PAIR_ENTITIES
• P_MAX_DTD_DEPTH
• P_CUSTOM_INTERNAL_ENTITIES