* [portfile functions] Override execute_process() to accept ALLOW_IN_DOWNLOAD_MODE option

* [vcpkg install] Set VCPKG_DOWNLOAD_MODE when using --only-downloads option

* [vcpkg_find_acquire_program] Allow in Download Mode

* Don't stop when build fails for a package

* Download sources for all packages in dependency graph

* Improve output messages

* Enable acquiring MSYS packages in download mode

* Documentation

* Update documentation

* execute_process() always fails on Download Mode

* Regenerate docs and fix formatting

* Run clang-format

* Use _execute_process on vcpkg_from_<source> helpers

* Fix calls to _execute_process() when not in Download Mode

This reverts commit 65d4bc146bf7c1c21989b680497b1f6f9a09c967.

* [portfile functions] Override execute_process() to accept ALLOW_IN_DOWNLOAD_MODE option

* [vcpkg install] Set VCPKG_DOWNLOAD_MODE when using --only-downloads option

* [vcpkg_find_acquire_program] Allow in Download Mode

* Don't stop when build fails for a package

* Download sources for all packages in dependency graph

* Improve output messages

* Enable acquiring MSYS packages in download mode

* Documentation

* Update documentation

* execute_process() always fails on Download Mode

* Regenerate docs and fix formatting

* Run clang-format

* Use _execute_process on vcpkg_from_<source> helpers

extra code comments. Maybe the test should actually try to link targets from the package instead  of just testing find_package

* [vcpkg]  post-build cmake test

- test for applications with cmake build system
- Add a test feature to vcpkg core, make progress for #72
- Tests for zlib, bzip2, libiconv and openssl for example
- Test for curl will be failed, because of a bug #3053
  It can detect a this type of problems

* [vcpkg_test_cmake] Add MODULE parameter to explicitly specify which type of integration to test.

* [bzip2] Fix casing of cmake module name