Suggestion: prebuild imports like in Gomacro

[Splizard]

In the GoMacro interpreter (https://github.com/cosmos72/gomacro), imported packages are compiled to Go plugins and then loaded dynamically, there is also a tool to recompile gomacro (such as on Windows which doesn't have plugin support).

This could be useful for yaegi, whether to squeeze out a little more performance or to simply workaround temporary interpreter bugs/limitations.