Updated Slovak translation.

Closes pull request #73.
typo
cosmetics
reduce variable scope
VSFilter: move the AboutDlg version to a new define and use that
AboutDlg.cpp: use the MPC_VERSION_ARCH define
Losslessly compress png images with https://github.com/subzey/zopfli-png and then with PNGGauntlet.
Compilation.txt: update GCC pack link
run astyle 2.03