[ENHANCEMENT] Create class methods to write tracks to file

[aweinert-MIT]

Relation

The script, RUN_uncor and RUN_terminal are good and simple script to introduce users to the encounter model classes and how to generate model samples or tracks derived from samples. However this script nor the the EncounterModel and UncorEncounterModel classes have the functionality to write the samples or tracks to file. This functionality existed in the previous default example scripts, RUN_1_emsample and RUN_2_sample2track and functions, em_sample and sample2track.

Description

• Create new method to enable UncorEncounterModel to write tracks to file
• Create new method to enable CorTerminalModel to write tracks to file

Per the convention guide, the files should be encoded in UTF-8 with linux style (\n) line endings

Additional

This issue is for tracks only, a issue #35 is for writing samples to file. UncorEncounterModel and CorTerminalModel both have track methods, they are implemented differently and do not share a EncounterModel superclass method for track; thus writing samples and tracks to files were organized into separate issues. While there is also no EncounterModel superclass method for sample, the desired functionality for issue #35 should be easier to implement and be flexible enough to write to file based on basic model parameters.

Lines 275 - 282 in sampletrack can be a good starting point for the new method.