Gowut v1.0.0 public release

Changes and new features in v1.0.0:

• Exported a new Writer which is used to render components.
  A value of this Writer is passed to Comp.Render().
  It is now possible to use components implemented entirely by you (this Writer is the last piece that was not exported previously), or you can now change the Render() implementation.
• Renamed all identifiers (constants and variables) to conform to the Go naming conventions (from UPPER_CASE to CamelCase).
  This is a backward incompatible change.
  Renaming rule is simple and consistent, for example CLR_RED => ClrRed, ETYPE_CLICK => ETypeClick etc.
• New methods in Server: SetHeader() and Header().
  You can use these to set HTTP response headers that will be added to all responses.
  For antecedent, see issue #10.
• Table.Add() now only ensures the table has enough rows, and enough cells in the row.
  Previously it called Table.EnsureSize() if the cell was nonexistent.
• New methods in Table: Trim() and TrimRow().
  These come handy for example if the table contains cells where colspan > 1 is set.
  By calling this method we can ensure no empty cells will be rendered at the end of such rows.
  For antecedent, see issue #11.
• Made changes to make it work on Google App Engine (GAE).
  Gowut and the Gowut "Showcase of Features" demo app can now be run on GAE.
  Live demo is available here: https://gowut-demo.appspot.com/show
• Other minor changes, improvements and optimization.