Support Satoshis only [for now]

[Daniel Cousens]

On a discussion with @Roasbeef, the suggestion was that msats will be too confusing in the short term, and

I don't really see msat being used for anything, at least in the short term

and

lnd always display sat, and accepts sat (on the rpc layer)

I propose, until the use cases come out, we temporarily drop the support and deal only in satoshis.

Thoughts @junderw ?

[Jonathan Underwood]

I agree. I have reverted to handling satoshis on wip branch

[jordodev]

I am using this great little library in a lightning wallet I'm developing but have noticed some merchants (eg. Blockstream store) are now encoding invoices in msats.

Could decoding support for millisatoshis be added?
Currently invoices with a 'p' divisor fail saying "Amount is outside of valid range"

[Jonathan Underwood]

@jordodev could you make a new issue please? Also provide any names of services already using mSats. Thanks.