This release is driven by wendelin.core v2 needs with one of the changes
being that now most of the library was moved into nogil code and can be
used fully from inside nogil world(*). Python modules are now just wrappers
of their nogil counterparts. The way for Python and nogil worlds to
communicate is also provided.

The move to nogil required many other enhancements along the way. Please
see CHANGELOG for overview.

The move to nogil brought some speedup automatically.
Below are benchmark results of this release compared to pygolang v0.0.4
(1573d101) for python-level benchmarks (we have only those at present):

	(on i7@2.6GHz)

thread runtime:

    name             old time/op  new time/op  delta
    go               18.3µs ± 0%  18.3µs ± 1%     ~     (p=1.000 n=10+10)
    chan             2.91µs ± 3%  2.99µs ± 5%   +2.73%  (p=0.022 n=10+10)
    select           3.57µs ± 3%  3.57µs ± 4%     ~     (p=0.720 n=9+10)
    def              55.0ns ± 0%  54.0ns ± 0%   -1.82%  (p=0.002 n=8+10)
    func_def         43.8µs ± 2%  44.1µs ± 1%   +0.64%  (p=0.035 n=10+9)
    call             64.0ns ± 0%  66.3ns ± 1%   +3.59%  (p=0.000 n=10+10)
    func_call        1.05µs ± 1%  1.24µs ± 0%  +17.80%  (p=0.000 n=10+7)
    try_finally       138ns ± 0%   137ns ± 1%   -0.51%  (p=0.003 n=10+10)
    defer            2.32µs ± 1%  2.63µs ± 1%  +13.52%  (p=0.000 n=10+10)
    workgroup_empty  38.0µs ± 1%  24.1µs ± 1%  -36.43%  (p=0.000 n=10+10)
    workgroup_raise  47.7µs ± 1%  28.2µs ± 0%  -40.76%  (p=0.000 n=10+10)

gevent runtime:

    name             old time/op  new time/op  delta
    go               16.9µs ± 1%  17.2µs ± 2%   +1.94%  (p=0.000 n=10+10)
    chan             7.43µs ± 0%  7.82µs ± 0%   +5.34%  (p=0.000 n=10+7)
    select           10.5µs ± 0%  11.2µs ± 0%   +6.74%  (p=0.000 n=10+10)
    def              63.0ns ± 0%  57.6ns ± 1%   -8.57%  (p=0.000 n=9+10)
    func_def         44.0µs ± 1%  44.2µs ± 1%     ~     (p=0.063 n=10+10)
    call             67.0ns ± 0%  64.0ns ± 0%   -4.48%  (p=0.002 n=8+10)
    func_call        1.06µs ± 1%  1.23µs ± 1%  +16.50%  (p=0.000 n=10+10)
    try_finally       144ns ± 0%   136ns ± 0%   -5.90%  (p=0.000 n=10+10)
    defer            2.37µs ± 1%  2.61µs ± 1%  +10.07%  (p=0.000 n=10+10)
    workgroup_empty  57.0µs ± 0%  55.0µs ± 2%   -3.53%  (p=0.000 n=10+9)
    workgroup_raise  72.4µs ± 0%  69.6µs ± 6%   -3.95%  (p=0.035 n=9+10)

workgroup_* changes for thread runtime is the speedup I am talking about.
defer/func_call slowdown is due to added exception chaining. We did not
optimize Python-level defer yet, and if/when that would be needed, it should
be possible to optimize by moving pydefer implementation into Cython.

(*) go and channels were moved into nogil world in Pygolang v0.0.3 +
v0.0.4 . Now it is the rest of the library that was moved with packages
like context, time, sync etc.

wendelin.core v2 needs nogil to run pinner thread on client side to
support isolation property in cooperation with wcfs: since there is a
`client -> wcfs -> pinner` loop:

      - - - - - -
     |           |
        pinner <------.
     |           |   wcfs
        client -------^
     |           |
      - - - - - -
     client process

the pinner thread would deadlock if it tries to take the GIL because
client thread can be holding GIL already while accessing wcfs-mmaped
memory (think doing e.g. `x = A[i]` in Python).