Implement conditions on tag

A condition is formed by:
    <tag> <op> <value>

<tag> is the normal yambar tag. <op> is one of '==', '!=', '<', '<=', '>', or
'>='. <value> is what you wish to compare it to.

'boolean' tags must be used directly. They falsehood is matched with '~':

    <tag>
    ~<tag>

Finally, to match an empty string, one must use ' "" ':
    <tag> <op> ""

doc/yambar-modules-i3.5.scd

@@ -102,10 +102,9 @@ bar:
         content:
           "":
             map:
-              tag: state
               default: {string: {text: "{name}"}}
-              values:
-                focused: {string: {text: "{name}*"}}
+              conditions:
+                (state == focused): {string: {text: "{name}*"}}
           current: { string: {text: "{application}: {title}"}}
 ```