Merge PR #1280: Implement simple transaction memos

* AltBytes -> Memo, memo CLI support & thread-through
* Check memo size, update changelog
* Update existing testcases
* Nuke CircleCI caches
* Charge gas proportional to memo size
* Fix gas allocations in ante handler testcases
* Add testcases
* Update changelog
* Fix tiny CLI bug & add to CLI tests
* Add '--memo' to gaiacli
* Add testcase for large memos
* Address PR comments

examples/kvstore/tx.go

@@ -22,6 +22,10 @@ func (tx kvstoreTx) GetMsg() sdk.Msg {
 	return tx
 }
 
+func (tx kvstoreTx) GetMemo() string {
+	return ""
+}
+
 func (tx kvstoreTx) GetSignBytes() []byte {
 	return tx.bytes
 }