use Devel::CheckLib, support LIBDIR= and INCDIR= args

Note that this still might fail on a multilib system, such as cc -m32
where the 32bit libs are not installed but the 64bit versions are.
Older Devel::CheckLib < 0.98 do not use the correct CFLAGS and LDFLAGS.

Add a proper Devel::CheckLib
0.05: add inc/Devel/CheckLib, improve POD, add README and some helper targets
fix -Wpointer-sign

Random.xs:50:35: warning: passing 'unsigned char *' to parameter of type 'const char *const'
converts between pointers to integer types with different sign [-Wpointer-sign]

        XPUSHs(sv_2mortal(newSVpv(rand_bytes, num_bytes)));
Merge branch 'master' of github.com:rurban/Crypt-OpenSSL-Random