math/readstat: new port - ead (and write) data sets from SAS, Stata, and SPSS

Originally developed for Wizard, ReadStat is a command-line tool and
MIT-licensed C library for reading files from popular stats packages. Supported
data formats include:

 * SAS: SAS7BDAT (binary file) and XPORT (transport file)
 * Stata: DTA (binary file) versions 104-119
 * SPSS: POR (portable file), SAV (binary file), and ZSAV (compressed binary)

Supported metadata formats include:

 * SAS: SAS7BCAT (catalog file) and .sas (command file)
 * Stata: .dct (dictionary file)
 * SPSS: .sps (command file)

There is also write support for all the data formats, but not the metadata
formats. The produced SAS7BDAT files still cannot be read by SAS, but feel free
to contribute your binary-format expertise here.

WWW: https://github.com/WizardMac/ReadStat