Fix for hang when sending large request with SSL enabled

When using SSL, we must use SSL_pending() in addition to/instead of select() to determine whether there is SSL data to be read.
This update makes the SSL_pending() function available and uses is to check for data if select() indicates there is no data.

See https://github.com/valenok/mongoose/issues/47

Inconsistent error codes of mg_get_var(..)

Made the names of the function arguments of the declaration and the definition of mg_get_var(..) the same.

Changed the error codes to have a consistent way of reporting errors. -2 is returned if there is a problem with the size of the destination buffer. -1 is returned if the variable is not found.

Updated the documentation of mg_get_var(..) in mongoose.h and removed the redundant comments from mongoose.c.

Added support for Ogg Vorbis audio files

Avoid some level-4 warnings issued by Visual Studio (2012 and possibly previous versions)

Changed signature of url_decode(): signalling on destination buffer overflow. mg_get_var() now does not require extra space for variable buffer

Suppress warning C4127 (conditional expression is constant) issued by Visual Studio 2012 introduced by FD_SET(..) which is using the do-while(0) trick.

Suppress warning C4204 (non-constant aggregate initializer) issued by Visual Studio 2012 due to missing C99 support.

Added declaration to avoid warning C4115 (named type definition in parentheses) issued by Visual Studio 2012.

Fix 30s hang->timeout when closing a socket with no more data

Fix 30s timeout when closing a socket that has no remaining data, introduced in 375950f6; setting the socket nonblocking makes recv() return instantly but not select()

Winsock2.h included after windows.h

Fixed an error in mongoose.c that caused a lot of errors where winsock2.h was included after windows.h

Add mime type for .xsl

Add default MIME type for xsl