Win32: Don't use PATH_MAX

This doesn't seem to be defined on windows. We only use it in one place
(DFZipFile.c). Just use a constant value of 4096 instead.
Win32: Don't use variables for array dimensions

GCC and clang both allow you to declare arrays whose size is a variable,
but this isn't supported in Visual C++. In DFZipFile.c, where we're
specifying the read & write buffer sizes, just use a constant numeric
value instead.
Win32: Avoid unicode escapes in string literals

In GCC and clang we can write escape sequences of the form \uXXXX in
strings to express unicode characters. However Visual C++ doesn't like
this - or, at least, it complains about the characters not being
supported in the current codepage.

There's only two instances in which we actually need to do this -
specifying the square and bullet characters for lists in Word. Just
store the UTF-8 encoded characters in an array, and use that instead.