Fileseq

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* go/cpp - Add support for printf (%04d) and houdini ($F04) pad syntax formats
* cpp - Prevent segfault when calling getters on default constructed FileSequence; return default values
* cpp - Define FileSequence::operator bool() to return FileSequence::isValid()
* cmd/seqls - Update to a faster parallel filesystem walk library
* go - Update to Go 1.15.x

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* cmd/seqls - Switch to a faster parallel filesystem walking library

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* Removed vendored Go dependencies
* Fix handling of Windows path separator in FileSequence.SetDirname and findSequencesOnDisk
* cmd/seqls - Properly build against gofileseq/v2
* cmd/seqls - Add --hash1 flag to use pad hash width=1 instead of 4
* cmd/seqls - Add --strict flag to apply strict length of search pattern pad character to matches
* cpp: Add a cmake build setup

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* Convert from Glide to Go module

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* Add Go module support as v2
* exp/cpp: cleanups of experimental go/cpp binding

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* Support a negative stepping value when start > end in frame range string pattern
* cpp: Prevent compiler warnings from int vs size_t