Fix issues with fields that are xs:simpleType.

There were two issues.

1) PHP doc for enum properties was wrong.

@property DTS\eBaySDK\Trading\Types\EnumStringType(string) $enumString

This is now corrected.

@property DTS\eBaySDK\Trading\Enums\EnumStringType(string) $enumString

2) Some eBay types are derived from xs:simpleType. XSLT was incorrectly
creating these as enums. These fields don't need to be a PHP class as
they can be represented with simple PHP types.
Merge branch 'simple-types' into develop
Ensure composer updates when running in travis.
Merge branch 'travis' into develop
Use develop branch of ebay-sdk.
Merge branch 'composer' into develop
Allow client code to get/set properties via element names.

Client code can choose to get and set object properties by using the
element name found in the XML.

Both lines below are valid:

$item->foo = 'foo';
$item->FOO = 'foo';
Merge branch 'element-names' into develop
Fix invalid PHP constants.

Some class constants were invalid PHP.

For example,

const NEW='new';

All constants are now prefixed with C_

For example,

const C_NEW='new';

In addition there is now phpunit tests for enum classes. This
should have been done from the start as running the tests would have
found this issue sooner.
Merge branch 'enums' into develop. Closes #2
Update code for 0.0.8 release.
Merge branch 'release-0.0.8'