.gitignore: Add file.
Read endpoints, spans and annotations from .csv file.

* src/importers.cpp
  (read_endpoint, read_span,
   read_annotations): New helper functions.
  (process_new): Read endpoints, spans and annotiations. Return spans range.

* src/zipkin_import.h
  (Importer): Add types for map and ranges, variables endpoints, spans,
      annotiations.
  (CSVImporter): Declare new private helper functions. Add exception type.

* src/import_tests.cpp
  (*_test): First basic unit tests for reading .csv files.

* test/annotations.csv
* test/endpoints.csv: New test files.