Change "R6RS" to "Guile"

[NalaGinrut]

Would you mind changing "R6RS" to "Guile" in the manual? Since Guildhall is a package manager of Guile, which implies the packages don't have to be a R6RS compatible one.

[ijp]

Some of the references in the docs refer to directories that dorodango creates, and so this may entail some code changes, if Wingo didn't already handle them all (probably did)
Note for later: files to change are

• overview.texi
• packaging.texi