Install on M1

[fredshone]

notes so far on installing on M1 mac:

brew install proj (perhaps also brew install some other spatial libs too)

If you get "AttributeError: dlsym(RTLD_DEFAULT, Error_GetLastErrorNum): symbol not found"

try:

export SPATIALINDEX_C_LIBRARY='/opt/homebrew/Cellar/spatialindex/1.9.3/lib'

from here

[brynpickering]

Mamba installable on M1 as of #192