main : alternative instruct mode (Vicuna support, etc.) (#863)

* Add support for configs, add configurable prefixes / suffixes, deprecate instruct mode, add stop prompt

* Add multiline mode, update text input.

* bugfix

* update implementation

* typos

* Change --multiline implementation to be toggled by EOF.

* bugfix

* default multiline mode

* add more configs

* update formating

* update formatting

* apply suggestions

configs/vicuna-simple.txt

@@ -0,0 +1,7 @@
+--interactive-first
+--keep -1
+--ins-prefix-bos
+--ins-prefix "\n### Human: "
+--ins-suffix "\n### Assistant: "
+--reverse-prompt "### Human: "
+--rm-trailing-space-workaround