More space-efficient text_order_sampling

Instead of storing values X for sample density s,
X/s is stored. This saves \log s bits per sampled
suffix.
Added text_order_isa_sampling_support

This policy class can be used when the SA sampling
policy is set to text_order_sa_sampling and the
sampling densities s_{SA} and s_{ISA} are equal.
Auto select the default select type of SA sampling.
Added Munro et al's space-efficient inverse perm.
A small program testing the performance of ISA access.
Test new isa_sampling strategies.
Unified interface for ISA sampling, added

static_asserts to check the template arguments.
Added new sampling strategy classes

 - `fuzzy_sa_sampling` and
 - `fuzzy_isa_sampling_support`
Put select_marked_sa in right class.
Changed output for experiments...
Included new sampling strategies into tests.
Fixed compile errors.
Added entropy calculation.
Removed statistic output.
Access to select_marked.
Merge remote-tracking branch 'origin/better_sampling'

Conflicts:
	include/sdsl/csa_sada.hpp
	include/sdsl/csa_wt.hpp
	test/CsaByteTest.cpp