[FEATURE] Adds inverse suffix array to ESA-Index.
[TEST] Tests creation of inverse suffix array.
[INTERNAL, COMMENT, TEST] Fixes some misaligned code. Reincludes tests for index creation.
[FEATURE] Parallelizes the inverse suffix array construction and uses reference to stringSetLimits of SA.
[INTERNAL] Simplifies function for inverse suffix array construction.
[INTERNAL] Changes range of splitter by using length of sa instead of isa.
Merge pull request #349 from rrahn/feature/index_isa

Feature/index isa