Make installable using pipx

[lllama]

pipx is a super useful way to install scripts into their own virtualenv. At the moment, it can make a good attempt at installing altimeter but doesn't set up the main scripts as these are defined as scripts in setup.py rather than console_scripts.

My suggestion is that that the scripts be converted to console_scripts to allow pipx to install them. (I appreciate I might be missing some of the reasons why this isn't possible.)