Meaning of "go to!" as an (old) exclamation

I found a fitting definition in the Oxford Dictionary:

archaic Said to express disbelief, impatience, or admonition.

The user that quoted from Oxford Dictionary is right. However I suspect the phrase was more nuanced than that. It's a highly idiomatic phrase (chiefly British) and has long fallen out of fashion and use. When used in the sorts of context you excerpted I believe it was a euphemistic way of telling someone to "go to hell." The connotation is much stronger, however, and in our modern parlance the phrase would be closer to telling someone to "f*** off." Notice how in your second excerpt the Saxon tells the knave to "go to, go to thy place." So "go to" is a shortened way of telling someone to "go somewhere," and that fact combined with the definition of the phrase as an expression of impatience or admonition makes me suspect makes me suspect "somewhere" is generally understood as hell.

The phrase "now go to" appears many times in the Bible (both old and new testaments), also in Shakespeare, and it definitely is not profanity or telling someone to go elsewhere in any rude manner. Keep in mind, the King James version of the Bible was translated into late middle English, so the phrase is likely a transliteration of some word or phrase in Hebrew, Aramaic or Greek. Definitely, it's idiomatic. Looking at the phrase in context, it probably equates to our contemporary "go for it", "get after it", "go do it", "do it" or "make it so".