Support customizing installation folder

[MatthewScholefield]

I'd like to install within Termux which has an entire userspace root at a relatively arbitrary location (due to android filesystem layout). So /opt is not writable and needs to be "$PREFIX/opt" instead. The guide says it requires hard coding the install path to /opt/wonderful which means it wouldn't work on Termux.

How difficult is it to remove all /opt/wonderful references? I know #33 briefly mentions it.

[asiekierka]

#33 and #34 are both required and sufficient to support customizing the installation folder.

Without #33, Pacman won't find the correct paths, but that's a relatively easy fix. The more annoying one is #34, as all binaries hardcode a dynamic library loader to be present in /opt/wonderful/lib at this time.