THis is necessary for newer Boost (1.71) which puts the exported targets
in Boost_LIBRARIES. If we export that verbatim it causes link issues on
projects using the config scripts from Make

This reverts commit e7294d81.

This does not exist on xenial yet

find_package is for use inside the *Config.cmake files

To add public dependencies to the generated config, use e.g.

list(APPEND ${PROJECT_NAME}_PUBLIC_DEPENDENCIES "Boost COMPONENTS system thread chrono")

fix issue that a double "-l" can appear in the Makefile config shell scripts for libraries which already contain the -l

This reverts commit 7eace484.

GNUInstallDirs doesn't really deliver the intended directories. CMAKE_INSTALL_LIBDIR e.g. points to lib/x86_64-linux-gnu on Ubuntu 16.04

Fixed the confusing and inconsistently used names *_LINK_FLAGS and *_LINKER_FLAGS by always setting and getting both variables

- Quotes around input variables when doing string replace avoid existing semicolons from being deleted.
- The project target library itself was missing in the linker flags.

fixed issue with compiler/linker flags being interpreted as lists and thus having semicolons in between

${PROJECT_NAME}_CPPFLAGS -> ${PROJECT_NAME}_CXX_FLAGS
${PROJECT_NAME}_LDFLAGS -> ${PROJECT_NAME}_LINK_FLAGS

also make sure that the exported lists are consistently space-separated (sometimes they might be semicolon separated or mixed)