Accessing a struct through an std::syn::MutexGuard using implicit
dereferencing can confuse the borrow checker. This situation arises when
obtaining mutable references to more than one field of the struct, which
is normally allowed.
https://doc.rust-lang.org/nomicon/borrow-splitting.html
However, when using implicit dereferencing, a mutable reference to the
the entire struct is taken. Thus, attempting to access another field in
this manner will lead to a compilation error.
https://doc.rust-lang.org/error-index.html#E0499
A simple way to avoid this is to first obtain a mutable reference to the
struct using explicit dereferencing.
The Features::new() method is nonsense and doesn't describe what
features were being set - we introduce an empty() and supported()
constructors instead.
This change was made in the flat features BOLT PR, as if a channel
requires some unknown feature bits we should still rumor it, we just
shouldn't route through it.
This merges local and global features into one struct, which is
parameterized by where it appers. The parameterization restricts
which queries can be made and which features can be set, in line
with the latest BOLT 9.
Closes#427.
