Does not capture Unicode chars under Windows

[malversan]

Currently in Windows the capture is made using msvcrt.getch(), which only captures one-byte at a time. This dramatically reduces the amount of characters that can be captured (along with producing bytes instead of chars, see issue #10).

Using msvcrt.getwch() instead produces multibyte captures and also returns chars instead of bytes.

So the code in PlatformWindows.getchars():

	def getchars(self, blocking=True):
		"""Get characters on Windows."""
		if blocking:
			yield self.msvcrt.getch()
		while self.msvcrt.kbhit():
			yield self.msvcrt.getch()

should be substituted with this:

	def getchars(self, blocking=True):
		"""Get characters on Windows."""
		def getchsequence():
			c = self.msvcrt.getwch()
			# Iteration is needed to capture full escape sequences with msvcrt.getwch()
			while c and c in self.keys.escapes:
				c += self.msvcrt.getwch()
			return c
		if blocking:
			yield getchsequence()
		while self.msvcrt.kbhit():
			yield getchsequence()

Tested in:
Windows 8.1, Python 3.6.1