spec(common): KMX+ binary format supporting LDML

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Introduction

Document an optimized binary format for use by the process_event #5015 and other consumers of LDML data. It will be written into the KMX binary file.

Goals

• new section is 64-bit aligned
• new section and header uses 64-bit offsets

implementation

• kmx_file.h - version16, kmx+ file header
• kmx+ optimized binary format
• in-memory structures for LDML keyboard

other

• json or xml streamers (dev use)
• binary streamer <-> into .kmx file (prod)
• use bson?

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Moved

This spec is now in-repo at https://github.com/keymanapp/keyman/blob/feature-ldml/core/src/ldml/C7043_ldml.md or eventually https://github.com/keymanapp/keyman/blob/master/core/src/ldml/C7043_ldml.md

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@mcdurdin simplifying starting assumptions if you want:

• could skip deduplicating strings
• could always use extend=1 in keys (i.e. always burn a string for each key)

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Changes:

• sections on 128 bit (0x10 byte) boundary for convenience
• added 4 byte reserved/padding on keys table so keys start on 128 bit boundary, and also for strs table

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Binary format done, minor tweaks but validated and useful.