BTSE: Various fixes (#1550)

* Common: DriveBy sanitisation of vars

* BTSE: Unify to exchange OrderLimits

* BTSE: Remove SeedAssets and test GetOrderExcutionLimit

* BTSE: Fix handling for K_* pairs

In addition to the M_ pairs we previously handled, BTSE has now
introduced K_* pairs (K_SATS-USD*).

This change moves the handling over to look for an exponent, and moves
the filtering to happen on all market data.
The original MarketSummary is still availiable, but I can't see any of
our current use-cases wanting to get the unfiltered list

* BTSE: Fix marketSummary futures field

BTSE returns no futures field for futures api marketInfo, and the documentation for the futures api shows returning false.
When we know we asked for futures, it makes the data flow much saner if
we can trust this field and not have to track what asset we asked for

* BTSE: Abstract marketPair.Pair()

* BTSE: Fix UpdateTicker symbol format

common/common.go

@@ -50,37 +50,28 @@ var (
 	_HTTPClient    *http.Client
 	_HTTPUserAgent string
 	m              sync.RWMutex
-	// ErrNotYetImplemented defines a common error across the code base that
-	// alerts of a function that has not been completed or tied into main code
-	ErrNotYetImplemented = errors.New("not yet implemented")
-	// ErrFunctionNotSupported defines a standardised error for an unsupported
-	// wrapper function by an API
-	ErrFunctionNotSupported  = errors.New("unsupported wrapper function")
-	errInvalidCryptoCurrency = errors.New("invalid crypto currency")
-	// ErrDateUnset is an error for start end check calculations
-	ErrDateUnset = errors.New("date unset")
-	// ErrStartAfterEnd is an error for start end check calculations
-	ErrStartAfterEnd = errors.New("start date after end date")
-	// ErrStartEqualsEnd is an error for start end check calculations
-	ErrStartEqualsEnd = errors.New("start date equals end date")
-	// ErrStartAfterTimeNow is an error for start end check calculations
-	ErrStartAfterTimeNow = errors.New("start date is after current time")
-	// ErrNilPointer defines an error for a nil pointer
-	ErrNilPointer = errors.New("nil pointer")
-	// ErrCannotCalculateOffline is returned when a request wishes to calculate
-	// something offline, but has an online requirement
-	ErrCannotCalculateOffline = errors.New("cannot calculate offline, unsupported")
-	// ErrNoResponse is returned when a response has no entries/is empty
-	// when one is expected
-	ErrNoResponse = errors.New("no response")
+	zeroValueUnix  = time.Unix(0, 0)
+)
 
+// Public common Errors
+var (
+	ErrNotYetImplemented      = errors.New("not yet implemented")
+	ErrFunctionNotSupported   = errors.New("unsupported wrapper function")
+	errInvalidCryptoCurrency  = errors.New("invalid crypto currency")
+	ErrDateUnset              = errors.New("date unset")
+	ErrStartAfterEnd          = errors.New("start date after end date")
+	ErrStartEqualsEnd         = errors.New("start date equals end date")
+	ErrStartAfterTimeNow      = errors.New("start date is after current time")
+	ErrNilPointer             = errors.New("nil pointer")
+	ErrCannotCalculateOffline = errors.New("cannot calculate offline, unsupported")
+	ErrNoResponse             = errors.New("no response")
+	ErrTypeAssertFailure      = errors.New("type assert failure")
+)
+
+var (
 	errCannotSetInvalidTimeout = errors.New("cannot set new HTTP client with timeout that is equal or less than 0")
 	errUserAgentInvalid        = errors.New("cannot set invalid user agent")
 	errHTTPClientInvalid       = errors.New("custom http client cannot be nil")
-
-	zeroValueUnix = time.Unix(0, 0)
-	// ErrTypeAssertFailure defines an error when type assertion fails
-	ErrTypeAssertFailure = errors.New("type assert failure")
 )
 
 // MatchesEmailPattern ensures that the string is an email address by regexp check