Latex math in pair_amoeba.rst

Equations described in the html pages generated from doc/src/pair_amoeba.rst of the develop GitHub branch (4/12/2023) seem to be not correctly expressed due to using an incorrect command \bold (should be \boldsymbol?) and no use of newline characters (and & for equation alignment).
Creating a PR or an issue for this small change is a bit high barrier for me. So let me report this here.

@yskmiyazaki Thanks for your note. This issue and a few related, minor formatting issues have been addressed and will be included in the next feature release.