Some fixes to make g++ *almost* compile ReaverLib.

Also update README a bit.

I'll try to keep ReaverLib compiling in reasonably new versions of GCC,
mostly because Mayfly does depend on it, and Mayfly looks like the one
piece of Reaver Project that got potentially usable quickly and might
draw some attention. Hopefully Despayre will also get there soon-ish.

I do not, however, plan to keep changing sane code just so it compiles
in GCC; Clang is still the main compiler, and if GCC builds work then
great, but if they don't, I'll wait for GCC to catch up.