updated add_biochar_pyrolysis (closes #171)

[BertoGBG]

Closes #171

Changes proposed in this Pull Request

update functions biochar pyrolysis. fixed error in investment cost and converted all units to tCO2e sequestered

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Data source for new technologies is clearly stated.
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the GPLv3 license.

[fneum]

Thanks! Could you highlight the unit changes in the release notes as a breaking change? I think it's ok as the feature is quite new, but generally we want to avoid units changing back and forth between versions.

Also please merge the upstream master and run compile_cost_assumptions once again. Thx!

[fneum]

Great, now it's just about resolving the merge conflicts and documenting the unit change in the release notes @BertoGBG!