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/readers/mod.rs

@@ -0,0 +1,11 @@
+/// Read in from csv.
+pub mod csv;
+
+/// Error definition for readers.
+mod error;
+/// Utilities to help with testing functionality using IO.
+/// Only meant for internal usage.
+#[cfg(test)]
+pub(crate) mod io_testing;
+
+pub use error::ReadingError;