Neatened things up to be more reader-friendly

[DeanTM]

Hey fellas. This isn't a proper pull request because I haven't done any tests (I'm not actually sure what to do re standards for this library?); rather, I've just I've just made the registrations.py file a little more reader-friendly.

Motivation

I'm trying to use ANTsPy to register light-sheet microscopy data of larval zebrafish brains, but am having limited success. I'm having to dig through the code to understand what arguments go where, which I find easier to do after renaming and reorganising a few things.

My hope is that now, if a person wants to understand a specific type of transform, they can read how the arguments args are constructed and work backwards from there.

What I've tweaked

• by comparing this Anatomy of an antsRegistration call post with the type_of_transform="antsRegistrationSyN[s]" case I was able to recover the full length names of some of the arguments; I used this to rename some arguments. I've also renamed some of the shorter-named variables.
• some of the variables had redundant or tautologous expressions, like if [Boolean Variable] == True, so I simplified those.
• I aligned the arguments in the list format so that they're easier to read (though possibly less PEP8-friendly).
• I've also noticed that the type of transform "SyNLessAggro" seems to do exactly the same as "SyNAggro", so I've added a comment to that in the function description.

[ntustison]

Thanks @DeanTM . I did a glance over and it looks pretty clean to me but I won't be able to do any testing until next week. If @cookpa and @stnava haven't approved of it by then, I'll work on merging it.