Use a new Super Famicom icon made by hi-ban.
data/pocketsnes_header.png: Optimise while leaving as 24bpp.
manual-en.txt: Fix a typo.
Add scaling to full-screen.

scaler.cpp, scaler.h: Add, from <https://github.com/dmitrysmagin/snes9x4d-rzx50>.

main.cpp: Handle the full-screen user preference.

menu.cpp: Re-enable the full-screen user preference.

manual-en.txt: Document.