Windows Support

[daurnimator]

Currently missing build system modifications. GNUmake is not well supported on windows.

Tested with MSVC 2015 and mingw-w64. https://ci.appveyor.com/project/daurnimator/luaossl/build/1.0.71

Mingw-w64

copy config.h.guess src\config.h
gcc -O2 -c -o src/openssl.o -IC:/projects/luaossl/env/include src/openssl.c -D_REENTRANT -D_THREAD_SAFE -DCOMPAT_PREFIX=luaossl -DHAVE_SYS_PARAM_H=0 -DHAVE_DLFCN_H=0 -D_WIN32_WINNT=0x0600 -IC:\OpenSSL-Win64/include -IC:\OpenSSL-Win64/include
gcc -O2 -c -o vendor/compat53/c-api/compat-5.3.o -IC:/projects/luaossl/env/include vendor/compat53/c-api/compat-5.3.c -D_REENTRANT -D_THREAD_SAFE -DCOMPAT_PREFIX=luaossl -DHAVE_SYS_PARAM_H=0 -DHAVE_DLFCN_H=0 -D_WIN32_WINNT=0x0600 -IC:\OpenSSL-Win64/include -IC:\OpenSSL-Win64/include
gcc -shared -o _openssl.dll src/openssl.o vendor/compat53/c-api/compat-5.3.o -LC:\OpenSSL-Win64/lib -LC:\OpenSSL-Win64/lib -llibeay32 -lssleay32 -lws2_32 -ladvapi32 -lkernel32 C:/projects/luaossl/env/bin/lua53.dll -lm

MSVC

copy config.h.guess src\config.h
cl /nologo /MD /O2 -c -Fosrc/openssl.obj -IC:/projects/luaossl/env/include src/openssl.c -D_REENTRANT -D_THREAD_SAFE -DCOMPAT_PREFIX=luaossl -DHAVE_SYS_PARAM_H=0 -DHAVE_DLFCN_H=0 -D_WIN32_WINNT=0x0600 -IC:\OpenSSL-Win64/include -IC:\OpenSSL-Win64/include
cl /nologo /MD /O2 -c -Fovendor/compat53/c-api/compat-5.3.obj -IC:/projects/luaossl/env/include vendor/compat53/c-api/compat-5.3.c -D_REENTRANT -D_THREAD_SAFE -DCOMPAT_PREFIX=luaossl -DHAVE_SYS_PARAM_H=0 -DHAVE_DLFCN_H=0 -D_WIN32_WINNT=0x0600 -IC:\OpenSSL-Win64/include -IC:\OpenSSL-Win64/include
link -dll -def:_openssl.def -out:_openssl.dll C:/projects/luaossl/env/lib/lua52.lib src/openssl.obj vendor/compat53/c-api/compat-5.3.obj -libpath:C:\OpenSSL-Win64/lib -libpath:C:\OpenSSL-Win64/lib libeay32.lib ssleay32.lib ws2_32.lib advapi32.lib kernel32.lib

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Closes #77

[daurnimator]

Unless anyone has objections (@wahern?) I'll merge this PR this week; leaving the build system to be completed in another PR. (with this PR luarocks will work, so some people will get utility there)