Compute image pixel density without performing rectangle intersection (+5 squashed commits)

Squashed commits:
[0e27904] Partially implement DPI calculation with rotation of the image

Fixes test suite
[a64f662] pageinfo: all tests pass
[c5b811a] Fix typos
[cdd2286] Can now find inline images for efficiently
[60dde8d] First cut at implementing intelligent DPI detection based on content stream

Broke many of the test cases

tests/test_pageinfo.py

@@ -103,8 +103,8 @@ def test_single_page_image():
     assert pdfimage['bpc'] == 8
 
     # DPI in a 1"x1" is the image width
-    assert pdfimage['dpi_w'] == 8
-    assert pdfimage['dpi_h'] == 8
+    assert abs(pdfimage['dpi_w'] - 8) < 1e-5
+    assert abs(pdfimage['dpi_h'] - 8) < 1e-5
 
 
 def test_single_page_inline_image():
@@ -131,4 +131,5 @@ def test_jpeg():
 
     pdfimage = pdfinfo[0]['images'][0]
     assert pdfimage['enc'] == 'jpeg'
+    assert (pdfimage['dpi_w'] - 150) < 1e-5