Add type method to mixers
Add validation of mixer
Add  #include <string> to mixer.hpp
Merge pull request #754 from rimms/validate-mixables

Validate mixables
fix wrong test of linear mixer
Eliminate unsed serialize: fixes #742
use scoped_r/wlock instead of scoped_lock for rw_mutex fix #769
Merge pull request #770 from jubatus/feature/fix-769

use scoped_wlock and scoped_rlock for rw_mutex
new feature unlearning
test compile ok, yet it does not success
append core/unlearn
add recommender_storage_base.hpp
Use unordered_map in inp function of local_storage instead of vector

The new key_manager uses unordered_map for id2key instead of vector.
We need to use unordered_map in inp method as the same way to calculate scores for all labels.
Write test for inp method after clear
Fix inp method for local_storage_mixutre same as local_storage
new feature unlearning
test compile ok, yet it does not success
Use unordered_map in inp function of local_storage instead of vector

The new key_manager uses unordered_map for id2key instead of vector.
We need to use unordered_map in inp method as the same way to calculate scores for all labels.
Write test for inp method after clear
Fix inp method for local_storage_mixutre same as local_storage