Merge branch 'develop' of https://github.com/joebauers/bitcoinbook into joebauers-develop

preface.asciidoc

@@ -19,7 +19,7 @@ _The best way to get the right answer on the Internet is not to ask a question,
 
 I hope you can help me find and publish the "right answer" by the time this book is ready to print.
 
-The early-realease source code is published on Github: https://github.com/aantonop/bitcoinbook
+The early-release source code is published on Github: https://github.com/aantonop/bitcoinbook
 
 File an "Issue", or fork, modify and create a "Pull Request" with your changes.
 
@@ -141,8 +141,8 @@ difficulty target::
 ((("target difficulty")))
  	A difficulty at which all the computation in the network will find blocks approximately every 10 minutes.
 
-difficulty re-targetting::
-((("difficulty re-targetting")))
+difficulty re-targeting::
+((("difficulty re-targeting")))
 	A network-wide re-calculation of the difficulty which occurs once every 2106 blocks and considers the hashing power of the previous 2106 blocks.
 	
 fees::