Implement new directives to control processRuleNames option

[elchininet]

This pull request implements new directives to control the processRuleNames option.

/*rtl:rules*/

This directive set the processRuleNames option to true in the next rule no mattering the value of the global processRuleNames option:

input

/*rtl:rules*/
.test1-ltr {
    background-image: url('/images/test1-l.png');
}

/*rtl:rules*/
.test1-rtl {
    background-image: url('/images/test1-r.png');
}

/*rtl:rules*/
.test2-left::before {
    content: "\f007";
}

.test2-right::before {
    content: "\f010";
}

output

[dir="ltr"] .test1-ltr {
    background-image: url('/images/test1-l.png');
}

[dir="rtl"] .test1-ltr {
    background-image: url('/images/test1-r.png');
}

[dir="ltr"] .test1-rtl {
    background-image: url('/images/test1-r.png');
}

[dir="rtl"] .test1-rtl {
    background-image: url('/images/test1-l.png');
}

/* These selectors will not be processed because only one of them has the rtl:rules directive */
.test2-left::before {
    content: "\f007";
}

.test2-right::before {
    content: "\f010";
}

/*rtl:begin:rules*/ and /*rtl:end:rules*/

These directives should be used together, they will provide the beginning and the end for processRuleNames blocks.

input

.test1-ltr {
    background-image: url('/images/test1-l.png');
}

.test1-rtl {
    background-image: url('/images/test1-r.png');
}

/*rtl:begin:rules*/
.test2-left::before {
    content: "\f007";
}

.test2-right::before {
    content: "\f010";
}
/*rtl:begin:rules*/

output

.test1-ltr {
    background-image: url('/images/test1-l.png');
}

.test1-rtl {
    background-image: url('/images/test1-r.png');
}

[dir="ltr"] .test2-left::before {
    content: "\f007";
}

[dir="rtl"] .test2-left::before {
    content: "\f010";
}

[dir="ltr"] .test2-right::before {
    content: "\f010";
}

[dir="rtl"] .test2-right::before {
    content: "\f007";
}

[coveralls]

coverage: 100.0%. remained the same
when pulling 2eb7e19 on add_rules_directive
into 349e04f on master.