Initial vim syntax for just

including:
- operators
- quotes/strings
- raw quotes/strings
- backtick sub-shells
- curly substitutions
- "set shell" handling

vim-just/example/justfile

@@ -0,0 +1,55 @@
+#!/usr/bin/env oh-no
+# vim:filetype=just
+
+set shell := ["python", "-c"]
+set something
+
+alias d := dogs
+
+export HOTDOGPARTY := hats
+
+now_ish := `print("oh gee")` + `print(sum([1, 2, 5]))`
+
+an_string := "sit ready \"for reals\" 'uh huh' {{an_raw_string + '{{what' }}"
+
+an_raw_string := 'sit ready "wow" {{not_gonna}}'
+
+hats := '''
+very serious hat's
+'''
+
+wats := """
+    {{an_string}} \"yay\" 'ok'
+
+  {{ 'dog' + just_executable()}}
+
+  {{justfile()}}
+
+  {{justfile_directory()}}
+
+{{arch()}} {{os()}}
+  """
+
+serious_business := ```
+from __future__ import print_function
+import os
+import datetime
+
+print(f"home: {os.environ.get("HOME", "?")}")
+print(f"now-ish: {datetime.datetime.now()}")
+```
+
+dogs: aminal manimal _secret
+
+# show the aminal by kind
+aminal kind='dog':
+  #!/usr/bin/env python
+  import sys
+  import os
+  print('\n'.join(os.environ.keys()), file=sys.stderr)
+
+_secret +WHATEVER='OK':
+  @echo "don't tell anyone {{WHATEVER}}"
+
+manimal:
+  @echo wow