Fix interface compatibility with php-opentracing beta6 for PHP 7 (ins…

…tana#1)

Fix interface compatibility with php-opentracing beta6 for PHP 7

fix method names for PHP<7 compatibility

The methods

- `InstanaSpanType::entry()`,
- `InstanaSpanType::local()` and
- `InstanaSpanType::exit()`

have been renamed to

- `InstanaSpanType::entryType()`,
- `InstanaSpanType::localType()` and
- `InstanaSpanType::exitType()`

to provide compatibility with PHP < 7.

Because the methods are API and introduce a BC break, I am bumping
the version to 2.0.0.

bump version

update version

Update version in UserAgent

fix false being treated as null

initial commit