dhall_rust/dhall/src/syntax/ast, branch substitutions

add type substitutions to serde_dhall

2021-04-10T20:59:07Z

this adds subsititutions, which work similar to the `Dhall.substitutions` mechanism of the Haskell dhall package, and which can be used e.g. like this: ```rust serde_dhall.from_str(...) .substitute_names(hashmap!["Newtype" => static_type]) .parse::()? ``` The idea behind this is to make it easy to add programmer-defined types which may be used in configs for programs, without forcing the program's users to re-import the same type definitions each time (or the programmers to keep the dhall-based definitions in sync with their rust types, since these are now generated automatically). Caveats so far: - makes some of the code ugly (dhall internals are now used in serde_dhall/src/lib.rs, for example) - haven't tested error messages so far - some unecessary copying of strings and static type values

Untangle caching code

2020-11-01T17:36:49Z

Prefer u64/i64 to usize/isize

2020-10-28T20:18:17Z

Make `SimpleValue` deserializable within other types

2020-10-27T23:33:26Z

Fixes https://github.com/Nadrieril/dhall-rust/issues/184

spec: Enable `with` optimizations

2020-09-14T22:19:49Z

spec: fix precedence of `===` and `with`

2020-06-25T14:12:09Z

Deserialize `Prelude.Map` and `toMap` to a map instead of a list

2020-04-10T11:10:53Z

Move duplicate field checking to parser

2020-04-07T10:19:36Z

Move BinOp and Builtin definitions in the relevant module

2020-04-06T21:26:08Z

Extract operation-related code to a new module

2020-04-06T21:11:54Z