Fix tests, fix blessings!

With the setupterm() singleton issue #33 worked around with pty.fork(), we can now be much more assured about our test cases. Several existing test cases that previously succeeded began to fail! Some failed simply because they were "corrected" to match the behavior discovered at that time, but was wrong. Others failed because of errors within blessings/__init__.py that were previously undiscovered.

Notably:
- warning emitted for subsequent Terminal() instances of different ``kind`` values, explaining the expected behavior.
- height and width always returns a digit, even without ttys (prevents TypeError)
- number_of_colors returns 0 when does_styling is False (prevents "setupterm() must first be called")
- NullCallableStrings return NullCallableStrings, resolving t.color(9)('shmoo') (prevents exception: unicode cannot be called)
- remove the pokemon curses.error silent handler (prevents exceptions from being missed!)
- as_subprocess decorator function executes the function in a child process of pty.fork(), the parent re-displays any exceptions thrown, asserts its exit value, etc. This ensures setupterm() is called once, freshly, for each child process.
- test_height_and_width_ioctl: set a window to a specific size, then assert the return values of t.height and t.width are correct, and not just integers.

Minors:
- assert no side-effects written to output stream where StringIO() is used. child processes that write to stdout will always be a "failed test case" as well, performing the same.
- many minor fixes to test cases, perhaps some behaviors you were not aware of, such as misspellings are not errors when the terminal is not a tty.
- check 0 and 8 number_of_colors than just 256, now that this is possible.
- new test cases for TypeError's, passing wrong parameters to capabilities (some of these may have been previously missed due to the pokemon exception handler)

that about sums it up, hope this suites better than the previous.