f0: remove toolchain specific options

While nano specs are certainly handy, it should be documented how to use them,
not turned on by default.  People with otherwise valid toolchains, who might
simply not care about nano specs are unable to build the examples with these
options.
gitignore netbeans project files

Just in case ;)
Bump libopencm3 submodule

No new examples require this, but it's a better base for stm32f0 and any lcd
work.