add example of a go block returning value through a channel
implement DroppingBuffer and SlidingBuffer
move implementation details under impl
expose buffers from csp module, but not Process and FnHandler
add timeout channel
use FixedBuffer if Channel is initialized with an integer
make main function in go_block example "return" a string
add put_then_callback & take_then_callback
add csp.no_op
fix race condition caused by Python's bad scoping rules
update http example