1.0.0-alpha.27 Rework generator and walker

Most of the changes of this release relate to rework of generator and walker. Instead of plenty methods there just single method for each one: generate() for the generator and walk() for the walker. Both methods take two arguments ast and options (optional for the generator). This makes API much simpler (see details about API in Translate AST to string and AST traversal):

Also List class API was extended, and some utils methods such as keyword() and property() were changed to be more useful.

Generator

• Changed node's generate() methods invocation, methods now take a node as a single argument and context (i.e. this) that have methods: chunk(), node() and children()
• Renamed translate() to generate() and changed to take options argument
• Removed translateMarkup(ast, enter, leave) method, use generate(ast, { decorator: (handlers) => { ... }}) instead
• Removed translateWithSourceMap(ast), use generate(ast, { sourceMap: true }) instead
• Changed to support for children as an array

Walker

• Changed walk() to take an options argument instead of handler, with enter, leave, visit and reverse options (walk(ast, fn) is still works and equivalent to walk(ast, { enter: fn }))
• Removed walkUp(ast, fn), use walk(ast, { leave: fn })
• Removed walkRules(ast, fn), use walk(ast, { visit: 'Rule', enter: fn }) instead
• Removed walkRulesRight(ast, fn), use walk(ast, { visit: 'Rule', reverse: true, enter: fn }) instead
• Removed walkDeclarations(ast, fn), use walk(ast, { visit: 'Declaration', enter: fn }) instead
• Changed to support for children as array in most cases (reverse: true will fail on arrays since they have no forEachRight() method)

Misc

• List
  • Added List#forEach() method
  • Added List#forEachRight() method
  • Added List#filter() method
  • Changed List#map() method to return a List instance instead of Array
  • Added List#push() method, similar to List#appendData() but returns nothing
  • Added List#pop() method
  • Added List#unshift() method, similar to List#prependData() but returns nothing
  • Added List#shift() method
  • Added List#prependList() method
  • Changed List#insert(), List#insertData(), List#appendList() and List#insertList() methods to return a list that performed an operation
• Changed keyword() method
  • Changed name field to include a vendor prefix
  • Added basename field to contain a name without a vendor prefix
  • Added custom field that contain a true when keyword is a custom property reference
• Changed property() method
  • Changed name field to include a vendor prefix
  • Added basename field to contain a name without any prefixes, i.e. a hack and a vendor prefix
• Added vendorPrefix() method
• Added isCustomProperty() method