changelog: add entry for pressure logic directionality work

changelog.txt

@@ -1,6 +1,15 @@
 Changelog
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+2017-10-19 (thetaepsilon)
+Directional flowables are now implemented.
+All devices for which it is relevant (valve, flow sensor etc.) have been converted so that they only flow on their connecting sides, so pressure propogation now works as expected for these devices when pressure logic is enabled.
+Classic mode continues to be preserved by default as before.
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 2017-10-14 (thetaepsilon, VanessaE)
 Node breakers have been updated to not have a tool by default, and determine if the node that they are trying to break can be dug with the tool in it's inventory slot.
 The crafting recipe for the node breakers has been updated, using a new gear crafting item that requires iron instead of mese, which should be a more accessible cost in most cases.