Improve FromBytes documentation and release 0.7.27

This PR adds examples to most methods of `FromBytes`, and
separately documents `derive(FromBytes)`. Theoretical soundness
requirements are placed with trait documentation, and the details
of the derive's analysis is placed in the derive documentation.

This PR follows the pattern of #505.

Makes progress towards #32.

Cargo.toml

@@ -15,7 +15,7 @@
 [package]
 edition = "2018"
 name = "zerocopy"
-version = "0.7.26"
+version = "0.7.27"
 authors = ["Joshua Liebow-Feeser <[email protected]>"]
 description = "Utilities for zero-copy parsing and serialization"
 license = "BSD-2-Clause OR Apache-2.0 OR MIT"
@@ -49,7 +49,7 @@ simd-nightly = ["simd"]
 __internal_use_only_features_that_work_on_stable = ["alloc", "derive", "simd"]
 
 [dependencies]
-zerocopy-derive = { version = "=0.7.26", path = "zerocopy-derive", optional = true }
+zerocopy-derive = { version = "=0.7.27", path = "zerocopy-derive", optional = true }
 
 [dependencies.byteorder]
 version = "1.3"
@@ -60,7 +60,7 @@ optional = true
 # zerocopy-derive remain equal, even if the 'derive' feature isn't used.
 # See: https://github.com/matklad/macro-dep-test
 [target.'cfg(any())'.dependencies]
-zerocopy-derive = { version = "=0.7.26", path = "zerocopy-derive" }
+zerocopy-derive = { version = "=0.7.27", path = "zerocopy-derive" }
 
 [dev-dependencies]
 assert_matches = "1.5"
@@ -75,6 +75,6 @@ testutil = { path = "testutil" }
 # CI test failures.
 trybuild = { version = "=1.0.85", features = ["diff"] }
 # In tests, unlike in production, zerocopy-derive is not optional
-zerocopy-derive = { version = "=0.7.26", path = "zerocopy-derive" }
+zerocopy-derive = { version = "=0.7.27", path = "zerocopy-derive" }
 # TODO(#381) Remove this dependency once we have our own layout gadgets.
 elain = "0.3.0"