feature request: covariates and ability to regress them

[Pradeep Reddy Raamana]

few ideas:

CSV input

• have column names, specify which columns are class, id, covariates and feature anmes!
• get the class ID from a specified colum (e.g. first, or specified)
• get the subject ID from a specified column (or the second or specified)

sbuject_id,class,feature1,feature2,age,sex
acbde_01,healthy,1.2,2.3,3.4,74,female
fghijk_01,healthy,1.2,2.3,3.4,76,male
...
lmnop_01,alzheimer,1.2,2.3,3.4,70,female
...
qrstu_01,depression,1.2,2.3,3.4,71,male

Directory of directories input

• covariates.txt in addition to features.txt within each subject folder

[Pradeep Reddy Raamana]

PR #51 fixes this.