Add Windows resource file support for shared libraries

Originally written by James Almer <jamrial@gmail.com>

With the following contributions by Timothy Gu <timothygu99@gmail.com>

* Use descriptions of libraries from the pkg-config file generation function
* Use "FFmpeg Project" as CompanyName (suggested by Alexander Strasser)
* Use "FFmpeg" for ProductName as MSDN says "name of the product with which the
  file is distributed" [1].
* Use FFmpeg's version (N-xxxxx-gxxxxxxx) for ProductVersion per MSDN [1].
* Only build the .rc files when --enable-small is not enabled.

[1] http://msdn.microsoft.com/en-us/library/windows/desktop/aa381058.aspx

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>