SD2 overdirve pedal simulation

the following packages are needed to build GxSD2Lead:

• libc6-dev
• libcairo2-dev
• libx11-dev
• x11proto-dev
• lv2-dev

note that those packages could have different, but similar names on different distributions. There is no configure script, make will simply fail when one of those packages isn't found.

$ make install

will install into ~/.lv2

$ sudo make install

will install into /usr/lib/lv2