Add 'chain time' and 'validator keycheck' commands.

docs/usage.md

@@ -325,6 +325,23 @@ Prior justified epoch: 3
 Prior justified epoch distance: 4
 ```
 
+#### `time`
+
+`ethdo chain time` calculates the time period of Ethereum 2 epochs and slots.  Options include:
+  - `epoch` show epoch and slot times for the given epoch
+  - `slot` show epoch and slot times for the given slot
+  - `timestamp` show epoch and slot times for the given timestamp
+
+```sh
+$ ethdo chain time --epoch=1234
+Epoch 1234
+  Epoch start 2020-12-06 23:37:59
+  Epoch end 2020-12-06 23:44:23
+Slot 39488
+  Slot start 2020-12-06 23:37:59
+  Slot end 2020-12-06 23:38:11
+```
+
 ### `deposit` comands
 
 Deposit commands focus on information about deposit data information in a JSON file generated by the `ethdo validator depositdata` command.
@@ -471,6 +488,18 @@ Balance:           3.201850307 Ether
 Effective balance: 3.1 Ether
 ```
 
+#### `keycheck`
+
+`ethdo validator keycheck` checks if a given key matches a validator's withdrawal credentials.  Options include:
+  - `withdrawal-credentials` the withdrawal credentials against which to match
+  - `privkey` the private key used to generat matching withdrawal credentials
+  - `mnemonic` the mnemonic used to generate matching withdrawal credentials
+
+```sh
+$ ethdo validator keycheck --withdrawal-credentials=0x007e28dcf9029e8d92ca4b5d01c66c934e7f3110606f34ae3052cbf67bd3fc02 --mnemonic='abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art'
+Withdrawal credentials confirmed at path m/12381/3600/10/0
+```
+
 ### `attester` commands
 
 Attester commands focus on Ethereum 2 validators' actions as attesters.