Redo the _whooollleee_ build system

Following the tutorials on http://www.ostricher.com/tag/scons/, I rebuilt the
build system so that SConscript files are *much* easier to write.

SConstruct

@@ -6,59 +6,15 @@
 #
 # Eryn Wells <eryn@erynwells.me>
 
-import os
-
-import erw
+import logging
 
+setup_logging()
 
 BUILD_CMDS = get_bool_argument(ARGUMENTS.get('BUILD_CMDS', False))
 MODE = ARGUMENTS.get('MODE', None)
 
-BUILD_DIR = Dir('#build')
-LIB_DIR = Dir('#lib')
-SRC_DIR = Dir('#src')
-TEST_DIR = Dir('#test')
-
-
-modes = {
-    'debug': erw.DebugEnvironment(succinct=not BUILD_CMDS),
-    'beta': erw.BetaEnvironment(succinct=not BUILD_CMDS),
-    'release': erw.ReleaseEnvironment(succinct=not BUILD_CMDS),
-}
-
 for mode in (MODE.split(',') if MODE else ['debug']):
-    try:
-        env = modes[mode]
-    except KeyError:
-        print 'Skipping invalid mode: {}'.format(mode)
-        break
-
-    out_dir = BUILD_DIR.Dir(env['NAME'])
-
-    # Allow same directory includes.
-    env.Append(CPPPATH=['.'])
-
-    # Process all lib dirs.
-    env['AVAILABLE_LIBS'] = {}
-    for lib in os.listdir(LIB_DIR.abspath):
-        lib_dir = LIB_DIR.Dir(lib)
-        if not lib_dir.isdir():
-            print 'Skipping {} in lib directory: is not a directory'.format(lib)
-            continue
-        lib_out_dir = out_dir.Dir('lib').Dir(lib)
-        output = do_sconscript(env, LIB_DIR.Dir(lib), lib_out_dir)
-        if not output:
-            print "Lib {} didn't return any object".format(lib)
-        env['AVAILABLE_LIBS'][lib] = output
-        env.Append(LIBPATH=[lib_out_dir])
-
-    # Get source files.
-    src_out_dir = out_dir.Dir('src')
-    do_sconscript(env, SRC_DIR, src_out_dir)
-    env.Append(LIBPATH=[src_out_dir],
-               CPPPATH=[SRC_DIR])
-
-    # Get test binaries.
-    test = do_sconscript(env, TEST_DIR, out_dir.Dir('test'))
-    run_tests = env.Alias('test', [test], '{} --gtest_color=yes'.format(test[0].path))
-    env.AlwaysBuild(run_tests)
+    env = Environment.for_mode(mode)
+    env.process_lib_dirs()
+    env.process_src()
+    env.process_tests()