Added MANUAL; updated README; renamed examples/ to samples/

I've made some minor fixes in stack.c and interpret.c

I've also added a manual (doc/MANUAL.md) and updated the README.md file.

The examples/ folder is now samples/, which I believe better describes what it
actually holds.

--HG--
rename : examples/LostKingdom.b => samples/LostKingdom.b
rename : examples/echo.b => samples/echo.b
rename : examples/hello.b => samples/hello.b
rename : examples/life.b => samples/life.b
rename : examples/sierpinski.b => samples/sierpinski.b