Use once_cell instead of lazy_static

[sigmaSd]

The motivation is that console already uses once_cell, so this should in theory decrease the total number of dependencies.

Note: The formatting has changed, do you happen to use some rustfmt flags? if so it would be better if you have a .rustfmt.toml file.

[djc]

The formatting changed because rustfmt usually doesn't work inside calls to macros, and you moved those constants out of macro context. So that's a good thing. Makes sense to me to make this change, thanks!

[sigmaSd]

I see, thanks as well

[djc]

(Note that #319 moves lazy_static to be for examples only, so if I figure out the regression it introduced we'll be able to do without once_cell for the library itself.)