add freebsd libradius sources

taken from https://www.gitorious.org/freebsd/freebsd/source/f1d6f4778d2044502209708bc167c05f9aa48615:lib/libradius
fix BSD related flags and defines
aviod use of netgraph lib
remove incompatible sockaddr_in attribute sin_len
replace srandomdev with srandom
fix moved include
add md5 hash lib

author: Alexander Peslyak (solar at openwall.com)
page: http://openwall.info/wiki/people/solar/software/public-domain-source-code/md5
use local md5 lib if openssl is not present

+ switch to unique naming for md5 functions
+ cmake based build
ignore build directory
add RADIUS accounting client/server examples
update readme