Fix resolution of included files and search paths in minibook (#25)

Author: p-costa

source/learn/building_programs/project_make.md

@@ -261,7 +261,7 @@ $2 ~ /^["'].+["']$/ {
     # count included files per file to avoid having duplicates in our list
     if (incc[FILENAME,$2]++ == 0) {
         # Add the included file to our list, this might be case-sensitive
-        inc[++ii] = sprintf("$(%s) += $(%s)", FILENAME, $2)
+        inc[++ii] = sprintf("$(%s) += %s", FILENAME, $2)
     }
 }
 
@@ -380,6 +380,10 @@ TEST_SRCS := src/tests/csv_read_test.f90 \
              src/tests/csv_test.f90 \
              src/tests/csv_write_test.f90
 
+# Add source and tests directories to search paths
+vpath % .: src
+vpath % .: src/tests
+
 # Define a map from each file name to its object file
 obj = $(src).o
 $(foreach src, $(SRCS) $(TEST_SRCS), $(eval $(src) := $(obj)))