Deprecate ``read`` and ``write``

[superbobry]

I think these two should be deprecated in favour of their path-based friends.

Three reasons:

• API should be as small as possible to be useful in 90% of the cases.

• The methods only work on file objects and produce ugly error messages when called on e.g. BytesIO:

  >>> import io
  >>> import marisa_trie
  >>> marisa_trie.Trie().write(io.BytesIO())
  Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "src/marisa_trie.pyx", line 193, in marisa_trie._Trie.write (src/marisa_trie.cpp:4201)
    self._trie.write(f.fileno())
  io.UnsupportedOperation: fileno

• A related method mmap lacks a file-based version.

@kmike, what do you think?