use pil resize

[geospatial-jeff]

• Uses PIL resize instead of skimage resize to lower memory footprint.
• Expose resampling method to caller

from PIL import Image

async with COGReader("http://async-cog-reader-test-data.s3.amazonaws.com/webp_web_optimized_cog.tif") as cog:
    tile = await cog.read(..., resample_method=Image.CUBIC)

Closes #56

[codecov-commenter]

Codecov Report

Merging #57 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #57      +/-   ##
==========================================
+ Coverage   95.53%   95.55%   +0.01%     
==========================================
  Files          11       11              
  Lines         762      765       +3     
==========================================
+ Hits          728      731       +3     
  Misses         34       34              

Impacted Files	Coverage Δ
aiocogeo/cog.py	97.72% <100.00%> (+0.01%)	⬆️
aiocogeo/partial_reads.py	95.32% <100.00%> (+0.05%)	⬆️

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