Updates: Mention SoupSessionFeature (and link to SoupLogger,

Updates: Mention SoupSessionFeature (and link to SoupLogger,

	* docs/reference/client-howto.xml: Updates: Mention
	SoupSessionFeature (and link to SoupLogger, SoupCookieJar, and
	SoupProxyResolverGNOME specifically). Mention forms and XML-RPC
	support. Mention header-parsing methods. Give a concrete example
	of connecting to SoupMessage signals. Document the (minimal)
	thread-safety guarantees

	* docs/reference/build-howto.xml: basic notes on pkg-config and
	#include usage.

svn path=/trunk/; revision=1238