Move headers to include/ dir

SConstruct

@@ -57,6 +57,7 @@ Export('env', 'build_type', 'prefix', 'version_info', 'test_xml')
 env.Append(CFLAGS = ['-Wall', '-Wextra', '-pipe', '-ggdb', '-pthread'])
 env.Append(LINKFLAGS = ['-O2', '-pthread'])
 env.Append(CPPDEFINES = ['_FILE_OFFSET_BITS=64'])
+env.Append(CPPPATH = ['#include'])
 
 if build_type == 'release':
     env.Append(CFLAGS = ['-O2'])
@@ -72,7 +73,8 @@ env.SConsignFile()
 
 subdirs = [
 'src',
-'test'
+'include',
+'test',
 ]
 
 for subdir in subdirs: