refactor build for tree of scons makefiles, fix out of source build, correct target handling

examples/echo_server/SConscript

@@ -0,0 +1,20 @@
+## echo_server
+##
+
+Import('env')
+Import('boostlibs')
+Import('wslib')
+Import('platform_libs')
+
+localenv = env.Clone ()
+
+sources = ["echo_server.cpp"]
+
+LIBS = [wslib, platform_libs] + boostlibs(['system',
+                                           'date_time',
+                                           'regex',
+                                           'thread'])
+
+prg = localenv.Program('echo_server', sources, LIBS = LIBS)
+
+Return('prg')