Fix doc warnings and doc cleanup in msgs.rs/ser.rs

[tnull]

This PR fixes a number of doc warnings, and since I was already touching the docs there I included some cleanups of the docs in msgs.rs and ser.rs.

Mostly nits, a lot of ticking and linking.

[codecov-commenter]

Codecov Report

Base: 90.73% // Head: 90.69% // Decreases project coverage by -0.04% ⚠️

Coverage data is based on head (cc3b4e6) compared to base (e8b91a4).
Patch coverage: 58.33% of modified lines in pull request are covered.

❗ Current head cc3b4e6 differs from pull request most recent head defa2f6. Consider uploading reports for the commit defa2f6 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1950      +/-   ##
==========================================
- Coverage   90.73%   90.69%   -0.05%     
==========================================
  Files          97       97              
  Lines       50540    50540              
  Branches    50540    50540              
==========================================
- Hits        45859    45836      -23     
- Misses       4681     4704      +23     

Impacted Files	Coverage Δ
lightning-invoice/src/lib.rs	87.48% <ø> (ø)
lightning/src/ln/channel.rs	88.76% <ø> (ø)
lightning/src/ln/msgs.rs	86.02% <ø> (ø)
lightning/src/ln/outbound_payment.rs	89.26% <ø> (ø)
lightning/src/ln/peer_handler.rs	55.82% <ø> (ø)
lightning/src/util/config.rs	65.90% <ø> (ø)
lightning/src/util/ser.rs	91.84% <ø> (ø)
lightning/src/util/ser_macros.rs	87.03% <58.33%> (ø)
lightning/src/chain/onchaintx.rs	94.33% <0.00%> (-1.05%)	⬇️
lightning-invoice/src/utils.rs	97.02% <0.00%> (-0.75%)	⬇️
... and 3 more

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[TheBlueMatt]

Feel free to squash.

[tnull]

Feel free to squash.

Just added another commit to fix building docs with --document-private-items.

[wpaulino]

Feel free to squash. CI failing with:

error: doctest failed, to rerun pass `--doc`
 --> src/util/ser_macros.rs:805:1
  |
3 | impl_writeable_tlv_based_enum!(EnumName,
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: consider importing this macro:
          lightning::impl_writeable_tlv_based_enum

[tnull]

Feel free to squash. CI failing with:
...

Ah, lol. Now hopefully fixed by squashing commits and including:

> git diff-tree -U2 e2f232ae cc3b4e6e
diff --git a/lightning/src/util/ser_macros.rs b/lightning/src/util/ser_macros.rs
index 9b4a6295..8d74a83a 100644
--- a/lightning/src/util/ser_macros.rs
+++ b/lightning/src/util/ser_macros.rs
@@ -802,5 +802,5 @@ macro_rules! _impl_writeable_tlv_based_enum_common {
 /// variants stored directly.
 /// The format is, for example
-/// ```
+/// ```ignore
 /// impl_writeable_tlv_based_enum!(EnumName,
 ///   (0, StructVariantA) => {(0, required_variant_field, required), (1, optional_variant_field, option)},

[tnull]

... and had to include two more ignores:

> git diff-tree -U1 cc3b4e6e defa2f68
diff --git a/lightning-invoice/src/lib.rs b/lightning-invoice/src/lib.rs
index 50ef3e4a..c01dfa47 100644
--- a/lightning-invoice/src/lib.rs
+++ b/lightning-invoice/src/lib.rs
@@ -808,3 +808,3 @@ impl SignedRawInvoice {
 ///
-/// ```
+/// ```ignore
 /// enum Enum {
@@ -829,3 +829,3 @@ macro_rules! find_extract {
 ///
-/// ```
+/// ```ignore
 /// enum Enum {

[TheBlueMatt]

Extra text in the []