feat: add git and history utility functions

- Add branch, fc, and gitup functions
- Update README documentation for new functions and abbreviations
- Remove obsolete push-vim function

functions/gitup.fish

@@ -0,0 +1,15 @@
+function gitup --description 'Fetch updates and show git status'
+    # Check if we are even in a git repository
+    if not git rev-parse --is-inside-work-tree >/dev/null 2>&1
+        echo "Check your map! You aren't in a git repository."
+        return 1
+    end
+    
+    if count $argv >/dev/null
+        git fetch $argv
+    else
+        git fetch
+    end
+    
+    and git status
+end