Redesign FormDataEncoder and FormDataDecoder

This patch was authored and released by @siemensikkema.

Redesign FormDataEncoder and FormDataDecoder to better align with Codable's intended behavior.

• Support decoding top level optionals (fixes #68)
• Adds a userInfo property to FormDataDecoder and FormDataEncoder
• More correct handling of "superDecoder" and "superEncoder"
• When nesting depth is exceeded we first fail when we’re actually trying to grab data from beyond the nesting limit
• Add some missing API docs

Fix regression that broke falling back to Codable

This patch was authored and released by @siemensikkema.

Fixes regression that broke falling back to Codable for types not conforming to MultipartPartConvertible (#66, fixes #65)

Note: this removes conformance of UUID to MultipartPartConvertible introduced in 4.2.0 because it is no longer needed.

Add support for encoding/decoding UUIDs

This patch was authored and released by @siemensikkema.

Add support for encoding and decoding UUIDs (#64)

Support nested multipart encoding

This patch was authored and released by @siemensikkema.

Add encoding and decoding support for nested objects (#57)

In order to avoid overflows by malicious actors there is a maximum nesting depth associated with FormDataDecoder. It defaults to 8 but is configurable in the initializer like so: FormDataEncoder(nestingDepth: 8).

This update also deprecates MultipartError.

Fix: MultipartParser cannot decode Non-ASCII header correctly

This patch was authored by @t-ae and released by @siemensikkema.

Fix the bug that MultipartParser cannot decode headers that contains non-ASCII characters correctly.

Optimize and simplify parser

This patch was authored by @siemensikkema and released by @0xTim.

Use more efficient parsing of multipart bodies to improve performance to near the level of the old C parser (~8% slower). Resolves #58 and replaces #59. Thanks to @edwellbrook for the initial test case and @weissi for help on parser performance 🙏🏻

Rewrite multipart parser in Swift

This patch was authored and released by @siemensikkema.

Rewrites parser in Swift and removes dependency on C library.

This also fixes an existing parsing bug where a nested multipart body would see its boundaries stripped of the "\r\n--" prefix. (replaces #56)

MultipartKit 4.0.0

With this release, MultipartKit is again extracted from Vapor itself so it can be used independently.

Docs:
https://docs.vapor.codes/4.0/content/
https://api.vapor.codes/multipart-kit/master/MultipartKit/

BUG FIX: Multipart/form-data crashed if data was missing

This patch was authored by @JaapWijnen and released by @siemensikkema.

Fix a crash in FormDataDecoderContext when the offset doesn't exist when parsing multipart form data ( vapor/vapor#2548 )

Fix date formatter availability in iOS

Adds iOS 10.0 to availability check for using ISO8601DateFormatter (#48).