Add instructions for building Tor with MSVC.

Written by "NewEraCracker" on ticket 13081; I've added a note that
this is not our preferred or supported build method.

doc/building-tor-msvc.txt

+Building Tor with MSVC.
+=======================
+
+NOTE: This is not the preferred method for building Tor on windows: we use
+mingw for our packages.
+
+Last updated 9 September 2014.
+
+
+Requirements:
+-------------
+
+ * Visual Studio 2010
+    http://go.microsoft.com/fwlink/?LinkId=323467
+ * CMake 2.8.12.2
+    http://www.cmake.org/download/
+ * Perl 5.16
+    http://www.activestate.com/activeperl/downloads
+ * Latest stable OpenSSL tarball
+    https://www.openssl.org/source/
+ * Zlib 1.2.8 tarball
+    http://zlib.net/
+ * Libevent 2.1 tarball
+    https://github.com/libevent/libevent/releases
+
+Make sure you check signatures on all these packages!
+
+Steps:
+------
+
+Building OpenSSL from source as a shared library:
+
+ cd <openssl source dir>
+ perl Configure VC-WIN32
+ perl util\mkfiles.pl >MINFO
+ perl util\mk1mf.pl no-asm dll VC-WIN32 >32dll.mak
+ perl util\mkdef.pl 32 libeay > ms\libeay32.def
+ perl util\mkdef.pl 32 ssleay > ms\ssleay32.def
+ nmake -f 32dll.mak
+
+Making OpenSSL final package:
+
+ Create <openssl final package dir>, I'd recommend using a name like <openssl source dir>-vc10.
+
+ Copy the following directories and files to their respective locations
+  <openssl source dir>\inc32\openssl => <openssl final package dir>\include\openssl
+  <openssl source dir>\out32dll\libeay32.lib => <openssl final package dir>\lib\libeay32.lib
+  <openssl source dir>\out32dll\ssleay32.lib => <openssl final package dir>\lib\ssleay32.lib
+  <openssl source dir>\out32dll\libeay32.dll => <openssl final package dir>\bin\libeay32.dll
+  <openssl source dir>\out32dll\openssl.exe => <openssl final package dir>\bin\openssl.exe
+  <openssl source dir>\out32dll\ssleay32.dll => <openssl final package dir>\bin\ssleay32.dll
+
+Building Zlib from source:
+
+ cd <zlib source dir>
+ nmake -f win32/Makefile.msc
+
+Building libevent:
+
+ cd <libevent source dir>
+ mkdir build && cd build
+ SET OPENSSL_ROOT_DIR=<openssl final package dir>
+ cmake -G "NMake Makefiles" .. -DCMAKE_BUILD_TYPE:STRING=RelWithDebInfo -DCMAKE_C_FLAGS_RELWITHDEBINFO:STRING="/MT /Zi /O2 /Ob1 /D NDEBUG" -DZLIB_LIBRARY:FILEPATH="<zlib source dir>\zdll.lib" -DZLIB_INCLUDE_DIR:PATH="<zlib source dir>"
+ nmake event
+
+Building Tor:
+
+ Create a dir above tor source dir named build-alpha and two subdirs include and lib.
+
+ Your build tree should now be similar to this one:
+  * build-alpha
+    - include
+    - lib
+  * <libevent source dir>
+    - build
+    - cmake
+    - ...
+  * <openssl source dir>
+    - ...
+    - ms
+    - util
+    - ...
+  * <openssl final package dir>
+    - bin
+    - include
+    - lib
+  * <tor source dir>
+    - ...
+    - src
+    - ...
+  * <zlib source dir>
+    - ...
+    - win32
+    - ...
+
+ Copy the following dirs and files to the following locations:
+  <openssl final package dir>\include\openssl => build-alpha\include\openssl
+  <libevent source dir>\include => build-alpha\include
+  <libevent source dir>\WIN32-Code\nmake\event2 => build-alpha\include\event2
+  <zlib source dir>\z*.h => build-alpha\include\z*.h
+
+ Now copy the following files to the followin locations:
+
+  <libevent source dir>\build\lib\event.lib => build-alpha\lib\libevent.lib
+  <openssl final package dir>\lib\libeay32.lib => build-alpha\lib\libcrypto.lib
+  <openssl final package dir>\lib\ssleay32.lib => build-alpha\lib\libssl.lib
+  <zlib source dir>\zdll.lib => build-alpha\lib\libz.lib
+
+ And we are now ready for the build process:
+
+  cd <tor source dir>
+  nmake -f Makefile.nmake
+
+ After the above process is completed there should be a tor.exe in <tor source dir>\src\or
+
+ Copy tor.exe to desired location and also copy zlib1.dll, libeay32.dll and ssleay32.dll from built zlib and openssl packages