Fixes #548, closes #551

This is so any 3rd-party definitions continue to work even if they have
MD5 checksums embedded.

A more secure hashing algorithm makes it less feasible to serve up a
modified tarball that matches the same checksum.

See the discussion in #548

add rbx-2.2.7

added definition of 1.9.3-p547

This reverts commit d45f1451, reversing
changes made to 13de5110.

Added definition of 2.0.0-p481

Ruby 2.1.2 is released!

link the latest log to /tmp/ruby-build.latest.log

Make the downloading message print the actual file name, not just the package name plus .tar.gz.

Correct the JRuby 9000 snapshot directory name.

`mktemp -t ruby-patch`, although working on OS X, fails on Travis CI
with the message "too few X's in template".

https://travis-ci.org/sstephenson/ruby-build/builds/23436088

[picture of I Have No Idea What I'm Doing dog]

https://travis-ci.org/sstephenson/ruby-build/builds/23435342

Filenames in git diff patches are prefixed by default by "a/" (source)
and "b/" destination. Such patches don't work with ruby-builds `--patch`
option since it internally uses `patch -p0`.

Prior workarounds were to use either an intermediate step:

    filterdiff --strip=1

or to generate the patch without the prefix in the first place:

    git diff --no-prefix ...

Now, git diff patches are detected by searching for this pattern:

    diff --git a/...

And `patch -p1` is used by default in such cases to strip the 1st
component of filename paths.

Fixes #521, closes #484

From patch(1):

    -f  or  --force
       Assume that the user knows exactly what he or she is doing, and do  not
       ask any questions.  Skip patches whose headers do not say which file is
       to be patched; patch files even though they have the wrong version  for
       the Prereq: line in the patch; and assume that patches are not reversed
       even if they look like they are.  This option does not suppress commen-
       tary; use -s for that.

Fixes #555

Prefer ggrep for grep invocations that use GNU extensions.

Fixes ruby-build on Solaris 11.1

Adding JRuby 1.7.12

OpenSSL library updated to 1.0.1g

Previous versions of the library contain a vulnerability CVE-2014-0160.

Link to releases in the Readme

Stop maintaining the changelog

All releases information has been migrated to GitHub Releases:
https://github.com/sstephenson/ruby-build/releases

This frees core contributors from having to maintain release notes in version
control, and regular contributors from wondering whether they need to edit
CHANGELOG while submitting a pull request.

Benefits of release notes being outside of version control are that they can be
edited post-release.