Rename method parameters and schedule columns

Renames following `ExchangeCalendar.schedule` columns:
- 'market_open' renamed 'open'
- 'market_close' renamed 'close'

Renames parameters of following `ExchangeCalendar` methods (as #61):
- `session_open`
- `session_close`
- `session_break_start`
- `session_break_end`
- `sessions_in_range`
- `is_session`
- `is_open_on_minute`
- `previous_open`
- `pervious_close`
- `next_open`
- `next_close`
- `previous_minute`
- `next_minute`

etc/make_exchange_calendar_test_csv.py

@@ -70,7 +70,7 @@
 
 df = pd.DataFrame(
     list(zip(cal.opens, cal.closes, cal.break_starts, cal.break_ends)),
-    columns=["market_open", "market_close", "break_start", "break_end"],
+    columns=["open", "close", "break_start", "break_end"],
     index=cal.closes.index,
 )