Add Handlebars syntax highlighting.

This is based on the HAML syntax highlighting. Of note is the loading of
the html highlighter since Handlebars is embedded in html.

rc/extra/hbs.kak

@@ -0,0 +1,75 @@
+# http://handlebarsjs.com/
+# ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+
+# Detection
+# ‾‾‾‾‾‾‾‾‾
+
+hook global BufCreate .*[.](hbs) %{
+    set buffer filetype hbs
+}
+
+# Highlighters
+# ‾‾‾‾‾‾‾‾‾‾‾‾
+
+addhl -group / regions -default html hbs  \
+    comment          {{!-- --}} '' \
+    comment          {{!   }}   '' \
+    block-expression {{    }}   '' 
+
+addhl -group /hbs/comment fill comment
+addhl -group /hbs/block-expression regex {{((#|/|)(\w|-)+) 1:meta
+
+# some hbs tags have a special meaning
+addhl -group /hbs/block-expression regex {{((#|/|)(if|else|unless|with|lookup|log)) 1:keyword
+
+# 'each' is special as it really is two words 'each' and 'as'
+addhl -group /hbs/block-expression regex {{((#|/|)((each).*(as))) 2:keyword 4:keyword 5:keyword
+
+addhl -group /hbs/block-expression regex ((\w|-)+)= 1:attribute
+
+# highlight the string values of attributes as a bonus
+addhl -group /hbs/block-expression regex ((\w|-)+)=(('|").*?('|")) 1:attribute 3:value
+
+# Commands
+# ‾‾‾‾‾‾‾‾
+
+def -hidden _hbs_filter_around_selections %{
+    # remove trailing white spaces
+    try %{ exec -draft -itersel <a-x> s \h+$ <ret> d }
+}
+
+def -hidden _hbs_indent_on_new_line %{
+    eval -draft -itersel %{
+        # preserve previous line indent
+        try %{ exec -draft <space> K <a-&> }
+        # filter previous line
+        try %{ exec -draft k : _hbs_filter_around_selections <ret> }
+        # copy '/' comment prefix and following white spaces
+        try %{ exec -draft k x s ^\h*\K/\h* <ret> y j p }
+        # indent after lines beginning with : or -
+        try %{ exec -draft k x <a-k> ^\h*[:-] <ret> j <a-gt> }
+    }
+}
+
+# Initialization
+# ‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+
+hook -group hbs-highlight global WinSetOption filetype=hbs %{ 
+    addhl ref hbs 
+    addhl ref html
+}
+
+hook global WinSetOption filetype=hbs %{
+    hook window InsertEnd  .* -group hbs-hooks  _hbs_filter_around_selections
+    hook window InsertChar \n -group hbs-indent _hbs_indent_on_new_line
+}
+
+hook -group hbs-highlight global WinSetOption filetype=(?!hbs).* %{ 
+    rmhl hbs 
+    rmhl html
+}
+
+hook global WinSetOption filetype=(?!hbs).* %{
+    rmhooks window hbs-indent
+    rmhooks window hbs-hooks
+}