Add several optimizer in R

[ziyeqinghan]

Add Adam, AdaGrad, AdaDelta optimizer in R and test them in mnist classification. Part of the test results are below.

• Adam optimizer with parameters learning.rate=0.001, optimizer="adam"

Batch [50] Train-accuracy=0.414375
Batch [100] Train-accuracy=0.571875
...
Batch [400] Train-accuracy=0.77541015625
Batch [450] Train-accuracy=0.788229166666667
[1] Train-accuracy=0.791672243040685
[1] Validation-accuracy=0.900841346153846
Batch [50] Train-accuracy=0.9034375
...
[5] Train-accuracy=0.965745192307692
[5] Validation-accuracy=0.96474358974359
Batch [50] Train-accuracy=0.971875
...
Batch [450] Train-accuracy=0.986423611111111
[10] Train-accuracy=0.986378205128205
[10] Validation-accuracy=0.972956730769231

• AdaGrad optimizer with parameters learning.rate=0.05, optimizer="adagrad"

Batch [50] Train-accuracy=0.576875
Batch [100] Train-accuracy=0.716484375
...
Batch [450] Train-accuracy=0.877534722222222
[1] Train-accuracy=0.879901632762313
[1] Validation-accuracy=0.947015224358974
Batch [50] Train-accuracy=0.94875
...
Batch [450] Train-accuracy=0.974982638888889
[5] Train-accuracy=0.975060096153846
[5] Validation-accuracy=0.969350961538462
Batch [50] Train-accuracy=0.9771875
...
Batch [450] Train-accuracy=0.984826388888889
[10] Train-accuracy=0.984909188034188
[10] Validation-accuracy=0.973056891025641

• AdaDelta optimizer with parameters optimizer="adam"

Batch [50] Train-accuracy=0.116875
Batch [100] Train-accuracy=0.24375
Batch [150] Train-accuracy=0.395208333333333
...
Batch [400] Train-accuracy=0.708984375
Batch [450] Train-accuracy=0.733871527777778
[1] Train-accuracy=0.741652168094218
[1] Validation-accuracy=0.950120192307692
Batch [50] Train-accuracy=0.9453125
...
[5] Train-accuracy=0.984124599358974
[5] Validation-accuracy=0.973657852564103
Batch [50] Train-accuracy=0.989375
...
Batch [450] Train-accuracy=0.994201388888889
[10] Train-accuracy=0.994190705128205
[10] Validation-accuracy=0.975460737179487

[terrytangyuan]

Looks great! Please resolve conflicts and we'll merge.

[ziyeqinghan]

The branch is rebased.

[terrytangyuan]

I cannot merge it if it doesn't pass tests :-(

[ziyeqinghan]

I don't know why cpp_test failed because I didn't change the c/c++ code. Could you gave me some suggestions? thank you so much!

[terrytangyuan]

@tqchen Could you take a look? I don't have permission to merge this and cannot rerun Travis for some reason

[terrytangyuan]

I rerun the tests but then it's outdated again...

[ziyeqinghan]

The branch is rebased again.

[terrytangyuan]

Thanks!