Highlighting of groups

[kshchepanovskyi]

optional, repeated keywords are not highlighted if thay are applied to groups:

syntax = "proto2";

package protostuff_unittest;

message A {
    optional int32 x = 1;

    optional group Group = 2 {

        optional int32 y = 1;

        repeated group NestedRepeatedGroup = 2 {
            optional int32 w = 1;
            optional int32 z = 2;
        }

        optional NestedMessage n = 3;

        message NestedMessage {
            repeated string s = 1;
        }
    }
}

Sample: