build: create and install a pkgconfig file

This adds trivial changes to the autotools infrastructur and a
template to generate and install a pkgconfig file libsodium.pc.
Merge pull request #66 from morfoh/pkgconfig

build: create and install a pkgconfig file
build: changed to only generate/install .pc file if pkg-config is found

This change improves the pkg-config support to only generate/install a .pc
file if pkg-config is found, assuming it is part of the build toolchain.

Note:

The minimal version set for pkg-config is 0.25, because this is the oldest
version I am able to test at the moment.
Ignore libsodium.pc
Make --disable-blocking-random and --disable-debug no-ops
Add pysodium
Requires at least autoconf 2.65
Bump Android NDK version
fix compile warnings

When compiling with [-Wold-style-declaration] on GCC, this warning appears:

  warning: ‘inline’ is not at beginning of declaration

This is easily fixed moving the INLINE directive at the very beginning of the declaration
fix compile warnings

When compiling with [-Wold-style-declaration] on GCC, this warning appears:

  warning: ‘inline’ is not at beginning of declaration

This is easily fixed moving the INLINE directive at the very beginning of the declaration
Merge branch 'master' of https://github.com/ctrix/libsodium
Merge pull request #73 from ctrix/master

fix compile warnings
Rename crypto_onetimeauth_poly1305_ref_implementation_name() prototype.
aes256-hongjun: move partial_precompute_tworounds() out of aes256.h
Add explicit "const" when casting pointers. No binary changes.
By Massimo Cetra.
Reindent aes256.h, remove commented code
aes256estream: don't assume that unaligned words can be read (for the input)
Quick quirk to support unaligned input for aes256estream.
Add newlines to .travis.yml
Ask Travis to compile with g++ as well