Replaced mmap with boost::interprocess::file_mapping (windows joins the game :-) )

Hi Hadley,

Great project! To support windows I replaced `mmap` with `boost:interprocess::file_mapping` / `mapped_region`.

After removing a bug (`string&` -> `char*`) in count_char.cpp it compiles on windows and ubuntu (travis).

`read_file`  and `read_lines` work,  but `read_csv` crashes.
Since I only replaced the memory mapping part and I'm not into the inner guts of fastread, I suspect that this was already a bug (especially since the current github version doesn't build on travis ci...), but I may be wrong.

Best,

Edwin