Git: add few bits to improve mergetool and diff

.gitconfig

@@ -21,10 +21,17 @@
 	smtpserver = smtp.gmail.com
 	smtpuser = robert.r.kmiec@gmail.com
 	smtpserverport = 587
-[diff]
-	tool = vimdiff
 [merge]
-	tool = vimdiff
+	conflictstyle = diff3
+	tool = nfugitive
+[mergetool "nfugitive"]
+	cmd = nvim -c "Gvdiffsplit!" "$MERGED"
+[diff]
+	tool = nvimdiff
+[difftool "nvimdiff"]
+	cmd = nvim -d "$LOCAL" "$REMOTE"
+[diff "markdown"]
+	xfuncname = "^#+.*$"
 [filter "lfs"]
 	clean = git-lfs clean -- %f
 	smudge = git-lfs smudge -- %f
@@ -33,13 +40,13 @@
 [alias]
 	cm = commit
 	co = checkout
-	br = branch
+	br = branch -vva
 	st = status
 	d = diff
 	dc = diff --cached
 	short = rev-parse --short --verify HEAD
 	update = !git stash && git pull --rebase && git stash pop && git submodule update --init --recursive
-	diff-image = "!f() { cd -- \"${GIT_PREFIX:-.}\"; GIT_DIFF_IMAGE_ENABLED=1 git diff \"$@\"; }; f"
+  diff-image = "!f() { cd -- \"${GIT_PREFIX:-.}\"; GIT_DIFF_IMAGE_ENABLED=1 git diff \"$@\"; }; f"
 [interactive]
 	diffFilter = delta --color-only
 [delta]
@@ -58,6 +65,8 @@
 	cmd = nvim -d $LOCAL $REMOTE $MERGED -c '$wincmd w' -c 'wincmd J'
 [init]
 	defaultBranch = master
-[diff "image"]
-	command = /home/kmcr/tools/git-diff-image/git_diff_image
-	textconv = imgcat
+#[diff "image"]
+#	command = /home/kmcr/tools/git-diff-image/git_diff_image
+#	textconv = imgcat
+[advice]
+	detachedHead = false