Various updates

[LadyChristina]

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Description

Made various changes - most importantly:

• Added a configurable parameter that specifies how many windows to look forwards and backwards when determining the population of active block producers in a given time period ('population_windows' in config.yaml)
• Made Ethereum parser more efficient by using generators instead of lists (because Ethereum block data was getting too large to handle that way)
• Updated the directory structure of the results and intermediate files
• Generalised max power ratio metric to concentration ratios
• Updated documentation

[ZeeshanJan]

LGTM