support for rawInclude and upgrade to pug-walk 0.0.3

[kavaro]

An error is thrown when the ast contains a rawInclude.
Upgrading to pug-walk 0.0.3 and adding the following visit function seems to fix the issue:

visitRawInclude: function(include) {
    this.bufLine('include');
    if (include.filter) {
      this.buffer(':' + include.filter + this.attrs(include.attrs));
    }
    this.buffer(' ');
    this.visit(include.file);
  }

Seems the above does not generate filter(s). I tried the following and it covers my use-case, though not sure whether this is ok in general. There seems to be an outdated ast format issue.

visitInclude: function(include) {
    this.bufLine('include');
    if (include.filters) {
      include.filters.forEach(function(filter) {
        if (filter.type === 'IncludeFilter') this.buffer(':' + filter.name);
      }, this);
      if (include.attrs) this.buffer(this.attrs(include.attrs));
    }
    this.buffer(' ');
    this.visit(include.file);
    this.visit(include.block);
  },

  visitRawInclude: function(include) {
    this.bufLine('include');
    if (include.filters) {
      include.filters.forEach(function(filter) {
        if (filter.type === 'IncludeFilter') this.buffer(':' + filter.name);
      }, this);
      if (include.attrs) this.buffer(this.attrs(include.attrs));
    }
    this.buffer(' ');
    this.visit(include.file);
  },