Implementation of attribute bp data and index

Created by: williamfgc

First working examples To do: Resolve conflicts (done) Resolve clang-format (done) Add tests after merging with current master (done)

examples/hello/bpAttributeWriter/CMakeLists.txt

+#------------------------------------------------------------------------------#
+# Distributed under the OSI-approved Apache License, Version 2.0.  See
+# accompanying file Copyright.txt for details.
+#------------------------------------------------------------------------------#
+
+if(ADIOS2_HAVE_MPI)
+  find_package(MPI COMPONENTS C REQUIRED)
+
+  add_executable(hello_bpAttributeWriter helloBPAttributeWriter.cpp)
+  target_include_directories(hello_bpAttributeWriter PRIVATE ${MPI_C_INCLUDE_PATH})
+  target_link_libraries(hello_bpAttributeWriter ${MPI_C_LIBRARIES})
+  
+else()
+  add_executable(hello_bpAttributeWriter helloBPAttributeWriter_nompi.cpp)
+  
+endif()
+
+target_link_libraries(hello_bpAttributeWriter adios2)