Restructured the way the various readers are implemented

This release reflects a major restructuring of the way readers and their channels are implemented. The changes were necessary to support unwrapped interferograms in isce2 format that have line interleaved single precision amplitudes and phases.This layout breaks all sorts of symmetries in the way tiles are extracted, the way zooming is implemented, and the way channels peek and decorate pixel values.

This release requires pyre later than pyre/pyre@37f6155

What's Changed

• Restructured the implementation of readers by @aivazis in #18

Full Changelog: v0.6.0...v0.7.0