anchor.diff:  Default "HelloWorld"
   -------------------------------------------------------------------------------
   
  -If we now run Tundra on this input, it will build our +HelloWorld+ executable:
  +If we now run Tundra on this input, it will build our +HelloWorld+ executable.
  +The output path shows that tundra has defaulted the variant to `debug` and the
  +subvariant to `default`.
   
   -------------------------------------------------------------------------------
   $ tundra
  
positive.code: sections are a reference of what you can place in the +Build+ block.
  Declarations within the block can appear in any order.
  
  === Units (required) ===
  
  The build block must contain a reference to a secondary file containing unit
  
negative.code: ==== Don't guess ====
  
  Tundra doesn't go out of its way to support auto-configuration of toolsets or
  guessing what compiler you want to use. It assumes you can list the
  configurations you care for up front. This speeds up incremental builds as no
  time is wasted scanning for tools in the environment every time.
  
  For a game project, there may be millions of builds between adding a new
  platform or configuration to a build system. Tools are also very brittle and
  need a specific configuration to produce working builds. The time it will take
  to support a new toolset will offset the time it takes to tell the build
  system about it by several orders of magnitude.
  
  == Hello, world ==
  
  A Tundra project needs atleast two files, one is +tundra.lua+ which specifies
  what build configurations are available for this project. Here is a sample
  minimal +tundra.lua+ file that creates a configuration +macosx-gcc+ which pulls
  in the stock +gcc+ toolset. We also say that this configuration is to be the
  default if nothing is specified when Tundra is run on Mac OS X:
  
  -------------------------------------------------------------------------------
  Build {
      Units = "units.lua",
      Configs = {
          Config {
              Name = "macosx-gcc",
              DefaultOnHost = "macosx",
              Tools = { "gcc" },
          },
      },
  }
  