Add lib/libradsec.h.

First sketch of the API.
Fix typo.
Thinking out loud some more.
Split libradsec.h in -base.h and -libevent.h.
Complete documentation for functions in libradsec-base.h.
Change the order of parameters to rc_connect() -- let those who may
default to 0 or NULL come last.
Cosmetic changes.
Rename libradsec-libevent.h --> libradsec-levent.h.
Low level connect and read working, kind of.  At least TCP.

Next: serializing.
First stab at a working blocking example.
Make git ignore gcc precompiled headers.
Improve API docu in libradsec-base.h slightly.

Still needs work!
Add a lost comment.
Add typedefs to use instead of enum to avoid ABI issues.

The size of an enum isn't well defined.
Rename rs_config to rs_handle.

A configuration will be something else.
Formatting changes.
Documentation changes.
Add licencing info.
Example client crafting simple packet using freeradius-libradius.
WIP on libradsec: 94e3f46 Example client crafting simple packet using freeradius-libradius.