~samwhited/xmpp

ref: a42ef11e9469b0b65746f979e1bdf5155d1c13dd xmpp/internal/saslerr d---------
all: update copyright message

[ci skip]
all: rewrap copyright comments/use xml.TokenReader
internal/ns: move ns package to internal/ns
Simplify slice literal declarations

[ci skip]
Use ns package in saslerr package
Return encoding errors from sasl errors
Minor updates to internal package comments

Update canonical import path of saslerr
Add TODO on idgen code
Add interface build-time checks for saslerr
Add experimental (internal) SASL errors package