fix various header regex, rename some processing variables, fix annot…

…ation plotting

implement inplace conversion for dac to save memory, and fix rdann sa…

…mpto case reading in one extra sample

fix dac over/underflow error

clean code

Refactor annotations library and change annotation attribute names

add memory saving options for reading signals

- Add GQRS ECG peak detectors

- Change and append plotrec input argument format
- Add 'signame' and 'sigsegments' attributes to MultiRecord class.
- Add shiftsamps input argument for rdann

- Enable reading/writing integer fs to headers and annotations when f…

…loat value is close enough

- Fix fs writing in wrann
- Add auto conversion to only write necessary annotation file bytes

- fix setup script

- add write functionality for custom ann types
- fix custom anntype reading
- fix problems with annotation writing

- Add capabilities to read and write all samples in records with mult…

…iple samples/frame

- Large refactor of _signals.py functions for reading dat files
- Reorganize tests and create additional ones for new functionality
- Create subfolders within package