Remove pyenv and add new shell theme

I enjoyed bobthefish quite a bit, but the nerd fonts on the CLI were
screwing up Emacs, and that's a non-starter for me.

One thing I like about cmorrell is that it has the host in the terminal
line, so I can tell which machine I'm on.

config/fish/functions/fish_mode_prompt.fish

@@ -1,8 +1,15 @@
-# This is handled inside fish_mode_prompt (see `__bobthefish_prompt_vi`)
-#
-# If you want to override this with your own mode prompt, disable bobthefish's
-# built-in mode prompt in your fish config:
-#
-#     set -g theme_display_vi no
-
-function fish_mode_prompt; end
+function fish_mode_prompt
+    if test "$fish_key_bindings" = "fish_vi_key_bindings"
+        or test "$fish_key_bindings" = "fish_hybrid_key_bindings"
+        switch $fish_bind_mode
+            case default
+                prompt_segment blue black "N"
+            case insert
+                prompt_segment green black "I"
+            case replace_one
+                prompt_segment red black "R"
+            case visual
+                prompt_segment magenta black "V"
+        end
+    end
+end