export `serde`, `rand` and `libc`; update version to 0.11.5

Increase version to 0.11.4

add `FromStr` implementation for key types

fix build.rs on Windows

bump version to 0.11.3

attempt to fix docs.rs docs

bump version to 0.11.2

Use correct flag on big endian machines.

This will fix `tests::sign` test case on mips/mips64. Verified with
`cross`[1] tool.

    cross test --target mips-unknown-linux-gnu
    cross test --target mips64el-unknown-linux-gnuabi64

Unfortunately this fix doesn't make `tests::test_debug_output` test case
pass, but this is about debug output so its not as critical as this
patch. See #63 for a discussion.

[1]: https://github.com/japaric/rust-cross

Revert "remove PublicKey::combine"

This reverts commit 17450e91.

Update version to 0.11

switch to 64-bit compilation; add flag for 32-bit

remove PublicKey::combine

add Debug impl to context object

add Display impl for the key types which outputs their hex representation

improve documentation

Since making PublicKey::serialize return a fixed-size array, this no longer
requires any allocation, so there's no reason not to have it.

Fix typo

Update a couple dependencies