v0.4.0

What's Changed

• Decimal: improve library by @ueco-jb in #55
• Pair: use max spread in bps by @ueco-jb in #57
• Pair: Add update_config message by @ueco-jb in #58
• Curve: distribution curve algorithm by @ueco-jb in #62
• Decimal: Replace wee-alloc in favor of soroban's one by @ueco-jb in #63
• CI: Add README coverage badge by @ueco-jb in #64
• Add Coverage badge to the readme by @ueco-jb in #65
• Pair: validate input parameters; fix single asset bug by @ueco-jb in #66
• Pair: add corner case checks and tests by @ueco-jb in #67
• Release v0.4.0 by @ueco-jb in #68

Full Changelog: v0.3.1...v0.4.0