Specialized type for Boolean sparse arrays

Recurrence matrices are wrappers of SparseMatrixCSC{Bool,Int}, which are useful to make some operations. However it is inefficient to create them (cf. #76), and also take more memory than what is needed (all nonzero values are true, so they don't add any information at all).

It would be useful to have a special type of sparse matrices for these cases, which only store row indices and the last index of each column - but not the values, with optimized methods. This might come in handy even for other applications, not only for recurrence analysis, so in my opinion it is worth to be in a separate package (outside JuliaDynamics).

I feel like investigating if such a package exists, and otherwise draft it. When it is working, we could use it to improve performance in this package.

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Start by reviewing the Boolean SparseMatrixCSC usage described here and issue #76, then investigate whether an existing Julia package provides a value-free sparse matrix type. If none exists, draft a separate package storing row indices and column endpoints, with optimized methods. Done means the package works and can be used to improve performance in RecurrenceAnalysis.jl.