use HTTPS URLs for the project

GitHub supports HTTPS. Use the secured URLs by default.
remove Gemfile.lock from Git
tests: switch to minitest 5

Adjust the test suite to support Minitest 5's syntax.

Minitest versions 4 and below do not support the newer Minitest::Test
class that arrived in version 5. For that case, use the
MiniTest::Unit::TestCase class as a fallback.
enabled `detect_encoding` for ruby 2
Replaced ruby version check by `method_defined?`
Merge pull request #64 from stephanvane/master

enable `detect_encoding!` for ruby 2
Remove libmagic dependency in favor of builtin binary detection

The builtin binary detection is likely less accurate than libmagic
in some ways, but will be more accurate in the more common cases.
remove libmagic source and patch
add another test case
scan the entire buffer for null bytes
only scan the first 10MB
make binary scan length configurable at runtime
update docs
add some more binary content types to sniffing
make png sniff a little more readable
add some more test fixtures
fix typo in comment
add some more fixtures to test UTF-16|32
Merge pull request #65 from brianmario/remove-libmagic

Remove libmagic dependency in favor of builtin binary detection
Merge pull request #60 from ktdreyer/rm-gemfile-lock

remove Gemfile.lock from Git