extract: escape ~ in package names

[sentriz]

consider packages from git.sr.ht, the user namespace is prefixed with ~

so running something like yaegi extract git.sr.ht/~emersion/scfg

was producing syntax errors with ~ in identifiers. and also ~ in filenames which worked but probably best not to have it there either

thanks!

[CLAassistant]

All committers have signed the CLA.

[ldez]

Hello, can you sign the CLA? Thank you.

[sentriz]

:+1: