Update README and add bLIP-0001

[ryanthegentry]

This PR initializes the new bLIPs repo with a README modeled after the BIPs README, and adds bLIP-0001, which was previously being discussed in PR #884 in the lightning-rfc repo.

Only a few adjustments have been made to bLIP-0001 while transferring from the previous repo:

1. added a mandated Universality section requesting proposals "discuss why the given feature is not intended to be
   universal and why it's still a good idea as a non-universal protocol" per @TheBlueMatt's feedback.
2. added that Feature Bits >100 yet <1000 were reserved for experimentation per @rustyrussell's comments in the 9/27 lightning-dev IRC meeting, and the same for TLVs > 65536 per Bolt #1.
3. fixed a few links/comments that would no longer be correct with a new bLIPs repo (hope I didn't miss any!).

Once these two docs are merged, the next step IMO will be to close the old PR and open a new one for a BOLT #13 (?) that acts as a central registry for bLIP'd Feature Bits, Message Types, and TLVs (and maybe more down the road...) per @t-bast's feedback (replacing PRs #605 and #716 from lightning-rfc). Maybe specifying the process of approving a bLIP using one of these resources, and then adding the resource assignment to the new BOLT, could be a good bLIP-0002?

[Roasbeef]

Carrying over my approval here from the other repo

LGTM ☄️

[dangershony]

Hi, I know I don't comment here much (I observe though) I am curious as to why is the b lower case? intuitively BLIP seems more inline with the BIP, BOLT systems. (apologies if this was discussed already).

[t-bast]

Agreed, I find bLIP kinda weird, not sure why it uses this casing.
And FWIW I voted for "sparks" 😎