Implement a generic read_csv method (#147)

* feat: Add interface to build `Matrix` from rows.
* feat: Add option to derive `RealNumber` from string.
To construct a `Matrix` from csv, and therefore from string, I need to be able to deserialize a generic `RealNumber` from string.
* feat: Implement `Matrix::read_csv`.

src/lib.rs

@@ -95,6 +95,8 @@ pub mod neighbors;
 pub(crate) mod optimization;
 /// Preprocessing utilities
 pub mod preprocessing;
+/// Reading in Data.
+pub mod readers;
 /// Support Vector Machines
 pub mod svm;
 /// Supervised tree-based learning methods