treemap: add a find_mut method
hashmap: add find_mut method
trie: add find_mut method
smallintmap: add find_mut method
expose find_mut in the Map trait
trie: improve docstring
rustdoc: Show purity
configure: error on unsupported target-triples and arm-linux-androideabi fix
kate: remove `const`, `log`, and `pure` keywords, add `super` keyword
configure: simplify pandoc version recognition.

The version recognition was failing for version 1.11, thinking the
minor version was 1 rather than 11.
core: Fix doc comment error, as per #4983
make ty_region give a useful span when it fails
auto merge of #5528 : thestinger/rust/find_mut, r=brson

This currently requires workarounds for the borrow checker not being flow-sensitive for `LinearMap` and `TrieMap`, but it can already be expressed for `TreeMap` and `SmallIntMap` without that.
auto merge of #5536 : sanxiyn/rust/doc-purity, r=brson

Fix #3804.
auto merge of #5537 : yichoi/rust/pull-0325, r=brson

In order to mitigate typo of target-triples, error notification of unsupported target triples which defined in mk/platform.mk added.

minor fix for arm-linux-androideabi added.
auto merge of #5539 : apasel422/rust/kate, r=brson
auto merge of #5540 : dbaupp/rust/configure-pandoc-version, r=brson

The version recognition was failing for pandoc version 1.11, thinking the
minor version was 1 rather than 11, and thus not building the documentation.
add deriving changes to release notes
auto merge of #5542 : catamorphism/rust/issue-4983, r=catamorphism
auto merge of #5538 : apasel422/rust/release-notes, r=sanxiyn