Update HarvestAPI.php

fix for "changing a user inside a project"

PUT /projects/#{project_id}/user_assignments/#{user_assignment_id}

http://www.getharvest.com/api/user-assignment#change-user-project
Updated HarvestAPI.php

fixed some typos in the functions:
    updateExpenseCategory
    updateExpense
    attachReceipt
    deleteInvoiceMessage
    deleteInvoicePayment
Update HarvestApi.php

Removed global namespace char in method getProjectEntries,
 from \Harvest_Range, to keep the class PHP5.2 compatible.
Merge pull request #1 from Rud5G/master

Fixed some typos in the api-urls