Update to latest stable release. This is a major version change from version 6 to 7.

Changes since last version:

• added .index_min() and .index_max();
• expanded ind2sub() to handle vectors of indices;
• expanded sub2ind() to handle matrix of subscripts;
• expanded expmat(), logmat() and sqrtmat() to optionally return a bool indicating success;
• faster handling of compound expressions by vectorise();
• added erf(), erfc(), lgamma();
• added .head_slices() and .tail_slices() to subcube views;
• eigs_sym(), eigs_gen() and svds() now use a built-in reimplementation of ARPACK for real (non-complex) matrices;
• spsolve() now requires SuperLU 5.2;

A build failure in mmseq was fixed and it was rebuilt to solve the Boost linker errors.