XEP-0114: external component authentication

New API xmpp_connect_component() introduced.
XEP-0114: minor fixes to auth.c

 - src/sha1.c is used instead of openssl;
 - xmpp_alloc/free should be used instead of malloc/free;
 - coding style fixes.
XEP-0114: Added an example for component connection.

The example is based on basic.c program.
To run the example, a configured server is needed.
added examples/component to .gitignore
examples: updated header in component.c