Issue #1258 - Part 1: Import mailnews, ldap, and mork from comm-esr52.9.1

mailnews/mime/jsmime/README.md

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+Code Layout
+===========
+
+JSMime is a MIME parsing and composition library that is written completely in
+JavaScript using ES6 functionality and WebAPIs (where such APIs exist). There
+are a few features for which a standardized WebAPI does not exist; for these,
+external JavaScript libraries are used.
+
+The MIME parser consists of three logical phases of translation:
+
+1. Build the MIME (and pseudo-MIME) tree.
+2. Convert the MIME tree into a list of body parts and attachments.
+3. Use the result to drive a displayed version of the message.
+
+The first stage is located in `mimeparser.js`. The latter stages have yet to be
+implemented.
+
+Dependencies
+============
+
+This code depends on the following ES6 features and Web APIs:
+* ES6 generators
+* ES6 Map and Set
+* ES6 @@iterator support (especially for Map and Set)
+* ES6 let
+* ES6 let-destructuring
+* ES6 const
+* Typed arrays (predominantly Uint8Array)
+* btoa, atob (found on global Windows or WorkerScopes)
+* TextDecoder
+
+Versions and API stability
+==========================
+
+As APIs require some use and experimentation to get a feel for what works best,
+the APIs may change between successive version updates as uses indicate
+substandard or error-prone APIs. Therefore, there will be no guarantee of API
+stability until version 1.0 is released.
+
+This code is being initially developed as an effort to replace the MIME library
+within Thunderbird. New versions will be released as needed to bring new support
+into the Thunderbird codebase; version 1.0 will correspond to the version where
+feature-parity with the old MIME library is reached. The set of features which
+will be added before 1.0 are the following:
+* S/MIME encryption and decryption
+* PGP encryption and decryption
+* IMAP parts-on-demand support
+* Support for text/plain to HTML conversion for display
+* Support for HTML downgrading and sanitization for display
+* Support for all major multipart types
+* Ability to convert HTML documents to text/plain and multipart/related
+* Support for building outgoing messages
+* Support for IDN and EAI
+* yEnc and uuencode decoding support
+* Support for date and Message-ID/References-like headers
+
+Other features than these may be added before version 1.0 is released (most
+notably TNEF decoding support), but they are not considered necessary to release
+a version 1.0.