Use new syntax highlighting engine from zyedidia/highlight

This changes all the syntax files in the runtime directory and also
changes how syntax highlighting is done from inside micro.

runtime/syntax/yaml.yaml

@@ -0,0 +1,32 @@
+filetype: yaml
+
+detect:
+    filename: "\\.ya?ml$"
+    header: "%YAML"
+
+rules:
+    - type: "(^| )!!(binary|bool|float|int|map|null|omap|seq|set|str) "
+    - constant:  "\\b(YES|yes|Y|y|ON|on|NO|no|N|n|OFF|off)\\b"
+    - constant: "\\b(true|false)\\b"
+    - statement: "(:[[:space:]]|\\[|\\]|:[[:space:]]+[|>]|^[[:space:]]*- )"
+    - identifier: "[[:space:]][\\*&][A-Za-z0-9]+"
+    - type: "([-\\w]+:\\s+)|([-\\w]+:$)"
+    - special:  "(^---|^\\.\\.\\.|^%YAML|^%TAG)"
+
+    - constant.string:
+        start: "\""
+        end: "\""
+        rules:
+            - constant.specialChar: "\\\\."
+
+    - constant.string:
+        start: "'"
+        end: "'"
+        rules:
+            - constant.specialChar: "\\\\."
+
+    - comment:
+        start: "#"
+        end: "$"
+        rules: []
+