Afmformats

- enh: implement `__setitem__` for `AFMSegment`
- ref: make `data` and `raw_data` private properties of `AFMSegment`

- enh: support .jpk-qi-series files (by extension)
- enh: improve error handling when data exported from the JPK software
does not contain encoder scaling offset and multiplier
- ref: use f-strings more often

- BREAKING CHANGE: "segment" column is no longer boolean, so it
cannot be used directly for indexing (15)
- fix: support modified AFM workshop file format (17)
- fix: segment data via `AFMData.appr` and `AFMData.retr` did not
use user-defined data to identify segments, but the "segment"
column from the raw data (this does not affect PyJibe or nanite which
fo not make excessive use of these properties)
- enh: add "segment count" key to meta data
- enh: optimize segment handling: new class AFMSegment that caches
segment indices (16)
- enh: properly test data types of metadata when setting them

- feat: generally support creep-compliance and stress-relaxation data
via the new "modalities" (supercedes "modality") recipe key
- feat: support for JPK creep-compliance data
- enh: extract segment duration from JPK files
- fix: ignore NaN values in JPK property files
- ref: add separate meta data section for modality-related keys
- ref: improvements of JPK metadata reader
- tests: rename test data files to reflect format

- docs: add section for implementing new file formats (13)
- fix: IndexError when trying to open .txt files that are no AFM files
- ref: separate submodule for formats

- enh: implement LazyMetaValue to speed-up loading JPK files
- enh: perform caching in LazyData (minor speed-up)