Fix base scalar multiplication

[paberr]

Description

Adds result of base scalar multiplication to self instead of discarding previous value. This seems to be the expected behaviour and this fixes the implementation of the pedersen hash.

closes: https://github.com/arkworks-rs/crypto-primitives/issues/109

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Before we can merge this PR, please make sure that all the following items have been checked off. If any of the checklist items are not applicable, please leave them but write a little note why.

• [x] Targeted PR against correct branch (master)
• [x] Linked to Github issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• [ ] Wrote unit tests
• [x] Updated relevant documentation in the code
• [x] Added a relevant changelog entry to the Pending section in CHANGELOG.md
• [x] Re-reviewed Files changed in the Github PR explorer

[paberr]

It seems like the checks on 052e094 were cancelled (possibly due to my changelog commit?).

[paberr]

Ok, seems to be some issue with the CI (potentially resource limits?). I've ran the tests agains curves locally and they pass.