Enable edition 2018

[tcharding]

Update the MSRV to Rust 1.41.1 and enable edition 2018.

Should not be merged without rust-bitcoin organization-wide planning on how to go about this upgrade.

Leaving as draft until rust-bitcoin Taproot release is done.

Discussion: rust-bitcoin/rust-bitcoin#510 (comment)

[tcharding]

Now includes version bump, please see #40 for discussion on the version format.

[apoelstra]

utACK 42a0a18

[tcharding]

Changes in force-push: rebase on master ignoring old appveyor config file, no other changes.

[tcharding]

... and fix up github actions CI job.

[apoelstra]

@tcharding are you able to merge this? I'm getting a weird error message from the merge script.

[tcharding]

Please note I made a change to the PR (I wanted to force push to run CI without AppVeyor)

Version is now 0.19.0-0.4.0 instead of 0.19.0-4.0.0. This implies the version of this lib is 0.4.0 (before this PR the version implied is 3). I'm going to merge without re-ACK, it can be changed before release if anyone wants to post merge NACK.

[tcharding]

My first try merging using the merge script. I had to hack it to skip bitcoin/depend from the output of git ls-tree -r HEAD. I don't fully understand what is going on in tree_sha512sum but I guessed that we don't want to include depend/bitcoin because it is a submodule.

[tcharding]

diff --git a/github-merge.py b/github-merge.py
index 2dc820d..3330dc0 100755
--- a/github-merge.py
+++ b/github-merge.py
@@ -162,6 +162,8 @@ def tree_sha512sum(commit='HEAD'):
for line in subprocess.check_output([GIT, 'ls-tree', '--full-tree', '-r', commit]).splitlines():
name_sep = line.index(b'\t')
metadata = line[:name_sep].split() # perms, 'blob', blobid
+        if metadata[1] == b'commit':
+            continue
assert(metadata[1] == b'blob')
name = line[name_sep+1:]
files.append(name)