add long and unsigned long ffi types
Changes: update
MANIFEST.SKIP: add file
add cpanm --notest option to speed up travis tests
travis: do not explicitly install Devel::CheckLib (it's included in dzil listdeps)
CompileTest.pm: compile with debug symbols
06-struct.t: fix dumb invalid memory accesses
add support for 64 bit ffi integer types on both 32bit and 64bit Perls

use Math::Int64 C API for marshalling/unmarshalling 64bit SV's
add Math::Int64 as submodule
add Math::Int64 build steps and dependencies
add Math::Int64 as explicit dependency in dist.ini
older perls do not support some bigint operator overloads

use Math::BigInt values explicitly in test comparisons
do not include Math::Int64 as submodule
Changes: update
t: indent
Changes: add note about 213ae61
travis: do not install libffi-dev since we bundle it
xs: update libffi
Changes: update
minor clean-up
v0.18

 - Add long and unsigned long ffi types (GH#7) (thanks, @calid!)
 - Add support for 64 bit ffi integer types (GH#9) (thanks, @calid!)
 - Fix invalid memory accesses in struct tests (should fix many failures)
 - Update libffi to 2f5b7ce
Revert "xs: update libffi"

This reverts commit 4c7dfc06ffadeec67c87c45da4dd95a68f0759d5.