add liftover methods

[jharenza]

Purpose

This PR adds gene symbol liftover methods

Issue

Closes #62

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Which areas should receive a particularly close look?

Is there anything that you want to discuss further?

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Pull review checklist

Unless otherwise noted above, this PR will be considered ready for review when all four items have been checked.

• All changes to text follow "one sentence per line" [Manubot instructions]
• All citations follow the Manubot citation instructions
• All changes or additions to tables follow the Manubot table instructions
• All figures follow the Manubot figure instructions
• There are no new spelling errors identified by the Manubot spellchecker

Spellcheck Step

The dictionary used for spellchecking can be updated.
Edit the file in build/assets/custom-dictionary.txt by adding new entries to the end.
You do not need to change anything else.
However, if you want to update the first line to have an accurate count of words and you want to remove non-unique ones, run the following command from within build/assets on your favorite OS X or Linux machine:

(( len = $(awk '!a[$0]++' < custom-dictionary.txt | wc -l ) - 1 )); tmpfile="$(mktemp)"; echo "personal_ws-1.1 en $len utf-8" > $tmpfile; tail -n +2 custom-dictionary.txt | awk '!a[$0]++' >> $tmpfile; mv $tmpfile custom-dictionary.txt

[jharenza]

hi @migbro this pr is ready for review when you get a chance :)

[github-actions]

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[github-actions]

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[migbro]

Need to update link, should probably update the repo to point at the specific file as well

[migbro]

Meant to request changes

[jharenza]

@migbro link is updated, thanks!

[github-actions]

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[github-actions]

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[rjcorb]

looks good to me!

[github-actions]

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@migbro skipped town ;) so @rjcorb did the re-review