Also build a shared library

SConstruct

@@ -9,6 +9,9 @@ version_info =  {
     'version_minor':  0 ,
     'version_patch':  0 ,
     'version_revision': revision,
+#version_abi is the abi version of the shared library. Only bump it when
+#backwards compatibility breaks. Strive to not break the ABI.
+    'version_abi':    '1.0.0' 
 }
 version_info['version_str'] = "%d.%d.%d.%s" % (
     version_info['version_major'],
@@ -99,6 +102,7 @@ env.Append(CFLAGS = ['-Wno-unused-parameter', '-Werror=implicit-function-declara
 env.Append(LINKFLAGS = ['-O2', '-pthread'])
 env.Append(CPPDEFINES = ['_FILE_OFFSET_BITS=64'])
 env.Append(CPPPATH = ['#include'])
+env.Append(SHLIBVERSION = version_info['version_abi'])
 
 if GetOption('force32bit'):
     env.Append(CFLAGS = ['-m32'])