316d8bcb01 Change all occurrences of "IO" to "I/O" (Jamil Lambert, PhD)
Pull request description:
Fixes#3871
ACKs for top commit:
tcharding:
ACK 316d8bcb01
apoelstra:
ACK 316d8bcb01504420a14854d2be122d1c8cffb4a9; successfully ran local tests; lgtm
Tree-SHA512: 437a95a1c36bcd4ae27aaacdfc5e0f3463e522a222c4a6ef2c3e234be4a24be2b600687bd58b300bf2b0a0d6596ab008f60903c91646458228eb34cf510908d6