Add new theme gianu

It's the gianu theme from oh-my-zsh but converted for oh-my-fish

themes/gianu/README.md

+## Gianu
+
+Original theme made by gianu for oh-my-zsh, converted to oh-my-fish by JBarberU
+
+![gianu theme](http://jbarber.se/images/gianu.png)
+
+
+#### Characteristics
+
+Displays:
+
+* Username and hostname
+* Working directory
+* Git information when available.

themes/gianu/fish_prompt.fish

+# name: Gianu
+function _git_branch_name
+  echo (command git symbolic-ref HEAD ^/dev/null | sed -e 's|^refs/heads/||')
+end
+
+function _is_git_dirty
+  echo (command git status -s --ignore-submodules=dirty ^/dev/null)
+end
+
+function fish_prompt
+  set -l cyan (set_color cyan)
+  set -l yellow (set_color -o yellow)
+  set -l red (set_color -o red)
+  set -l green (set_color -o green)
+  set -l white (set_color -o white)
+  set -l normal (set_color normal)
+
+
+  set -l cwd $cyan(basename (prompt_pwd))
+
+  if [ (_git_branch_name) ]
+    set -l git_branch $green(_git_branch_name)
+    set git_info "$normal($green$git_branch"
+
+    if [ (_is_git_dirty) ]
+      set -l dirty "$yellow ✗"
+      set git_info "$git_info$dirty"
+    end
+
+    set git_info "$git_info$normal)"
+  end
+
+  echo -n -s $normal '[' $white (whoami) $normal '@' $red (hostname -s) $normal ' ' $cwd ' '  $git_info $normal ']$ ' 
+end
+