* remove injection hook for textfile metrics, convert them to prometheus format
* add support for summaries
* add support for histograms
* add logic for handling inconsistent labels within a metric family for counter, gauge, untyped
* change logic for parsing the metrics textfile
* fix logic to adding missing labels
* Export time and error metrics for textfiles
* Add tests for new textfile collector, fix found bugs
* refactor Update() to split into smaller functions
* remove parseTextFiles(), fix import issue
* add mtime metric directly to channel, fix handling of mtime during testing
* rename variables related to labels
* refactor: add default case, remove if guard for metrics, remove extra loop and slice
* refactor: remove extra loop iterating over metric families
* test: add test case for different metric type, fix found bug
* test: add test for metrics with inconsistent labels
* test: add test for histogram
* test: add test for histogram with extra dimension
* test: add test for summary
* test: add test for summary with extra dimension
* remove unnecessary creation of protobuf
* nit: remove extra blank line
Ben Ye