initial fixes for building kj/main.c++ utilities on mingw
redefine ERROR from windows.h as a global constant in windows-sanity.h
fix writeLineToFd for windows console output

This function now (on windows):
* converts \n to \r\n (for both file and console outputs)
* when the output is redirected to a file, uses WriteFile with utf-8 output
* when the output will appear on a console, uses WriteConsole with utf-16 output instead
use KJ_STACK_ARRAY for win32 text buffers in main.c++
Merge pull request #122 from joshuawarner32/fix-mingw-build

initial fixes for building kj/main.c++ utilities on mingw