IMPORTANT added linting configuration

linting can be started by clicking Addins in RStudio, then
"Lint current file". This commit also contains quick fixes for common
linter messages like changing F to FALSE and T to TRUE.

.lintr

@@ -0,0 +1,11 @@
+linters: linters_with_defaults(
+    line_length_linter(150),
+    commented_code_linter = NULL,
+	object_name_linter = NULL,
+	brace_linter = NULL
+  )
+exclusions: list(
+    "inst/doc/creating_linters.R" = 1,
+    "inst/example/bad.R",
+    "tests/testthat/exclusions-test"
+  )