extras, doc: Remove strpack
Merge pull request #2511 from pao/topic/remove-strpack

Remove strpack from extras
fix #2560, export/using segfault
add ability to overlap tuple length with type tag. disabled by default.
more efficient codegen for typeassert
fix #1474, incorrectly replacing method with different static parameters
Merge branch 'master' into anj/linalg2