Thrombopoietin (TPO) Receptor Agonist Eltrombopag in Combination with Azacitidine (AZA) for Primary Treatment of Int-1, Int-2 and High-Risk Myelodysplastic Syndromes (MDS) Patients with Thrombocytopenia: Outcomes from the Randomized, Placebo-Controlled, Phase III SUPPORT Study