Class Extension

Just a collection of attributes that describes an extension
module and everything needed to build it (hopefully in a portable
way, but there are hooks that let you be as unportable as you need).

Instance attributes:
  name : string
    the full name of the extension, including any packages -- ie.
    *not* a filename or pathname, but Python dotted name
  sources : [string]
    list of source filenames, relative to the distribution root
    (where the setup script lives), in Unix form (slash-separated)
    for portability.  Source files may be C, C++, SWIG (.i),
    platform-specific resource files, or whatever else is recognized
    by the "build_ext" command as source for a Python extension.
  include_dirs : [string]
    list of directories to search for C/C++ header files (in Unix
    form for portability)
  define_macros : [(name : string, value : string|None)]
    list of macros to define; each macro is defined using a 2-tuple,
    where 'value' is either the string to define it to or None to
    define it without a particular value (equivalent of "#define
    FOO" in source or -DFOO on Unix C compiler command line)
  undef_macros : [string]
    list of macros to undefine explicitly
  library_dirs : [string]
    list of directories to search for C/C++ libraries at link time
  libraries : [string]
    list of library names (not filenames or paths) to link against
  runtime_library_dirs : [string]
    list of directories to search for C/C++ libraries at run time
    (for shared extensions, this is when the extension is loaded)
  extra_objects : [string]
    list of extra files to link with (eg. object files not implied
    by 'sources', static library that must be explicitly specified,
    binary resource files, etc.)
  extra_compile_args : [string]
    any extra platform- and compiler-specific information to use
    when compiling the source files in 'sources'.  For platforms and
    compilers where "command line" makes sense, this is typically a
    list of command-line arguments, but for other platforms it could
    be anything.
  extra_link_args : [string]
    any extra platform- and compiler-specific information to use
    when linking object files together to create the extension (or
    to create a new static Python interpreter).  Similar
    interpretation as for 'extra_compile_args'.
  export_symbols : [string]
    list of symbols to be exported from a shared extension.  Not
    used on all platforms, and not generally necessary for Python
    extensions, which typically export exactly one symbol: "init" +
    extension_name.
  swig_opts : [string]
    any extra options to pass to SWIG if a source file has the .i
    extension.
  depends : [string]
    list of files that the extension depends on
  language : string
    extension language (i.e. "c", "c++", "objc"). Will be detected
    from the source extensions if not provided.