Release notes
Custom delimiters in exported DNA sequences
Added ability to control delimiter symbols in exported DNA sequence files, both delimiters between IDT fields (`;` in the example below) and between DNA sequences of different domains (`-` in the example below), e.g.,

Which exports this line to a file: `strand 1;/5Biosg/-AAAAAAAA-CCCC/ISp9/CCCC-GGGGGGGG;25nm;STD`.
Distinction between internal modifications that attach to a base, versus those between bases
Some internal modifications are attached to a base (e.g., internal biotin on a T: [`/iBiodT/`](https://www.idtdna.com/site/catalog/modifications/product/1105)) versus those that go in between bases (e.g., a spacer such as [`/ISp9/`](https://www.idtdna.com/site/catalog/modifications/product/1391)). Previously the web interface assumed all internal modifications are of the former type, and also assumed they could be attached to any base. Now in the web interface (as in the Python package), one can distinguish between these two types, and for modifications attached to a base, can specify a subset of bases that they can attach to (e.g., IDT's internal biotin may only be on a T base):

Commits
- d00fe82: bumped version (David Doty) [916](https://github.com/UC-Davis-molecular-computing/scadnano/pull/916)
- c219170: Update CONTRIBUTING.md (David Doty) [916](https://github.com/UC-Davis-molecular-computing/scadnano/pull/916)
- 0ef4f44: fixes 912: customize delimiter between domains in exported DNA sequences (David Doty) [914](https://github.com/UC-Davis-molecular-computing/scadnano/pull/914)
- c9698af: closes 913: handle internal modifications that go in between bases (David Doty) [915](https://github.com/UC-Davis-molecular-computing/scadnano/pull/915)
- eff3768: fixed edit mod dialog to account for base vs. linker (David Doty) [915](https://github.com/UC-Davis-molecular-computing/scadnano/pull/915)