uCON64 Code (SVN)

- Added MinGW-w64 build support, including libdiscmage and libcd64.
- Added 64-bit Visual C++ (2015 & 2019) build support, including libdiscmage
and libcd64.
- Improved 64-bit support in general, but disabled FAL code on 64-bit
platforms (contains 32-bit integer to pointer hacks).
- All code compiles without warnings with GCC 9.2.

- Removed "experimental" DexDrive support. Experiment failed. The underlying
code had nothing to do with DexDrive.
- Updated htdocs to reflect current status in SVN.

- Removed "experimental" DexDrive support. Experiment failed. The underlying
code had nothing to do with DexDrive.

- Some cosmetic fixes.

- Disabled warnings added in newer GCC versions that are unwanted at this time
or have shockingly broken diagnostic code resulting in spurious warnings. For
uCON64 code disabled:
-Wimplicit-fallthrough
-Wformat-truncation
-Wstringop-overflow
For libdiscmage disabled:
-Wimplicit-fallthrough
-Wstringop-overflow
The unfortunate side-effect is that for older GCC versions a warning or error
will result in 3 or 2 extra lines stating that the options are not recognized.
Thanks to Philipp Seiler for pointing me to build logs at opensuse.org.

- Fixed warning about (correctly) passing 0 as size to memset() for certain
(newer?) GCC versions.
- Fixed drop_privileges() to truly drop all privileges (saved UID and GID)
when called after drop_privileges_temp().

- Fixed bug I introduced in n64_chksum(). This time for real.

- Fixed bug I introduced in n64_chksum().

- Fixed DJGPP specific issue in mem_hexdump().

- Removed extra newline after calling dm_nfo().