Adding code to deduct network fee from creditingOutputs, adding sanityChecks

src/main/scala/org/bitcoins/core/wallet/builder/TxBuilderError.scala

@@ -50,4 +50,41 @@ object TxBuilderError {
     */
   case object NoSigner extends TxBuilderError
 
+  /** Means that you specified a fee that was too large for the change output you provided.
+    * This may happen if you have a transaction with a lot of inputs, or the change output you provided
+    * is a output that contains a very small amount of bitcoin.
+    * */
+  case object FeeToLarge extends TxBuilderError
+
+  /** Means that the [[TxBuilder.destinations]] outputs you specified when creating the [[TxBuilder]] are NOT
+    * all included in the final signed tx
+    */
+  case object MissingDestinationOutput extends TxBuilderError
+
+  /** Means that you provided a outpoint in the [[TxBuilder.utxoMap]] that does not
+    * exist inside of [[TxBuilder.creditingTxs]]. You cannot spend an outpoint that was not
+    * passed into the txbuilder originally
+    */
+  case object MissingCreditingTx extends TxBuilderError
+
+  /** Means that the signed version of this transaction has MORE outputs than what was specified
+    * when building the [[TxBuilder]]. [[TxBuilder.destinations]] && [[TxBuilder.changeOutput]] should
+    * be the only outputs in the signedTx
+    */
+  case object ExtraOutputsAdded extends TxBuilderError
+
+  /** Means that the transaction spends outpoints that were not given when creating
+    * the [[TxBuilder]], aka, we should only spend outpoints in [[TxBuilder.outPoints]]
+    */
+  case object ExtraOutPoints extends TxBuilderError
+
+  /** Means that this transaction attempts to print satoshis out of thin air */
+  case object MintsMoney extends TxBuilderError
+
+  /** Means that the fee was not within the given range of error for [[TxBuilder.feeRate]]
+    * This might mean that the transactions pays a much larger fee than what was given as the [[TxBuilder.feeRate]] parameter, or a
+    * much smaller fee
+    */
+  case object BadFee extends TxBuilderError
+
 }

src/main/scala/org/bitcoins/core/wallet/fee/FeeUnit.scala

@@ -0,0 +1,22 @@
+package org.bitcoins.core.wallet.fee
+
+import org.bitcoins.core.currency.Satoshis
+
+/** This is meant to be an abstract type that represents different fee unit measurements for
+  * blockchains
+  */
+sealed abstract class FeeUnit
+
+/** Meant to represent the different fee unit types for the bitcoin protocol
+  * [[https://en.bitcoin.it/wiki/Weight_units]]
+  */
+sealed abstract class BitcoinFeeUnit
+
+case class SatoshisPerByte(satoshis: Satoshis) extends FeeUnit
+
+/** A 'virtual byte' (also known as virtual size) is a new weight measurement that
+  * was created with segregated witness (BIP141). Now 1 'virtual byte'
+  * has the weight of 4 bytes in the [[org.bitcoins.core.protocol.transaction.TransactionWitness]]
+  * of a [[org.bitcoins.core.protocol.transaction.WitnessTransaction]]
+  */
+case class SatoshisPerVirtualByte(satoshis: Satoshis) extends FeeUnit