Feature/population centers

using these points instead of the provinces' centroid should be a better approximation of actual heat demand, since centriods are more northern and showed cooler temperatures, thereby overestimating heat demands.

pop_centers = {
    "Quebec": (45.53312807333965, -73.61511415981778), # Montreal
    "Newfoundland and Labrador": (47.55902628296887, -52.740148813553624), # St. Johns
    "British Columbia": (49.26885406028422, -123.11713372323813), # vancouver
    "Nunavut": (63.747654358220444, -68.5170967002665), # Iqualit
    "Northwest Territories": (62.45269464084662, -114.36896850628257), # Yellowknife
    "New Brunswick": (46.09989553810743, -64.77416722665333), # Moncton
    "Nova Scotia": (44.64958366154484, -63.58093792618714), # Halifax  
    "Saskatchewan": (50.449703126577795, -104.61930722801765), # Regina
    "Alberta": (51.03649663454597, -114.07009597159944), # Calgary
    "Prince Edward Island": (46.242364438015976, -63.12712300014809), # Charlottetown
    "Yukon": (60.71835688260373, -135.05313593078967), # Whitehorse
    "Manitoba": (49.8908370535123, -97.13705628523745), # Winnipeg
    "Ontario": (43.75668261210348, -79.43114766451536), # Toronto
}

closes #2 (closed)