* Drop the iso_checksum_type & iso_checksum_url fields

In favor of simply using iso_checksum that will know what to do.

* fix after master merge

* Update builder_test.go

* Update builder_test.go

* Update builder_test.go

* Update builder_test.go

* Update builder_test.go

* remove checksum lowercasing tests

* Update builder_test.go

* Update builder_test.go

* better docs

* Update builder_test.go

* even better docs

* Update config.go

* Update builder_test.go

* Update step_create_vmx_test.go

* make generate

* better docs

* fix imports

* up tests

* Update _ISOConfig-required.html.md

* Update builder_test.go

* don't use sha1.Sum("none") as a caching path

* Update builder_test.go

* better docs

* Update iso_config_test.go

remove ISOChecksumType/ISOChecksumURL references

* Update step_download_test.go

* add iso_checksum_url and iso_checksum_type fixers + tests

* add concrete examples of checksum values

* add examples of checksumming from local file

* update go-getter dep

* up deps

* use new go-getter version

* up ESX5Driver.VerifyChecksum: use go-getter's checksumming

* ISOConfig.Prepare: get checksum there in case we need it as a string in ESX5Driver.VerifyChecksum

* Update iso_config.go

* get go-getter from v2 branch

* Update driver_esx5.go

add more comments

* Update driver_esx5.go

* show better error message when the checksum is invalid

* Update builder_test.go

put in a valid checksum to fix tests, checksum is md5("packer")

* Update builder_test.go

test invalid and valid checksum

* more test updating

* fix default md5 string to be a valid md5

* TestChecksumFileNameMixedCaseBug: use 'file:' prefix for file checksumming

* Update iso_config_test.go

* Update iso_config_test.go

* Update builder_test.go

* Update builder_test.go

* Update builder_test.go

* Update CHANGELOG.md

* Update CHANGELOG.md

* Update go.mod

* Update go.mod

* Update CHANGELOG.md