Process annotations file

Read annotations file in gtf format and parse free_text column. Also implement reverse parsing of free text columns to free_text column for writing new annotations back to gtf file.

Use pandas to read tab separated gtf file. Map key value pairs in free_text column first to dictionary and then create columns in dataframe per key. When mapping back to free_text column not every key may have a value. Delete key/value pairs where the value is empty.

Check that generated gtf file adheres to gtf standard specification.