Import the selection of integer types into boost::gil namespace,
  and move from channel.hpp to typedefs.hpp for easier access.
Replace bits32f with float32_t and bits64f with float64_t
  - kept as alias of scoped_channel_value.
Move float64_t (bits64f) to typedefs.hpp.
Replace the four {float|double}_{zero|one} min/max channel values
  with float_point_zero and float_point_one templates.
Replace <boost/cstdint,hpp> with C++11 <cstdint>.

Introduce preference of using declaration instead of typedef.
Reformat typedefs.hpp to take advantage of the using declaration
  - works much better for left-to-right reading, alias name as
    most important detail comes first.
Add some of missing #include typedefs.hpp, sort some headers.