Data model improvements

src/reader/cif/data-model.ts

src/reader/cif/schema.ts

src/reader/cif/text-field.ts

src/reader/common/column.ts

src/reader/common/text/column/fixed.ts

src/reader/common/text/tokenizer.ts

src/reader/gro/parser.ts

src/reader/spec/cif.spec.ts

src/reader/spec/fixed-column.spec.ts

src/script.ts