Improve parameter normalization/key hashing

[engisalor]

Custom key creation and parameter dict normalization here can be improved.

These functions are in part necessary due to a requests-cache issue. It's been addressed and this topic should be reassessed after the fix is included in its next release (1.0.0?).

While the requests-cache fix will improve URL handling, a custom key creation function is likely still needed to fully account for how Sketch Engine GET requests work. E.g., normalizing CQL strings will reduce functionally equivalent API calls.

• The simplest but most pervasive issue is stripping unnecessary spaces: alemma, "sandwich" == alemma,"sandwich".
• Requires a suite of tests to ensure that changes to normalization avoid unwanted side effects.