MAINT: Style check *.c and *.h files

"cpplint" was introduced pandas-devgh-14740, and
this commit extends to check other *.c
and *.h files in the pandas repo.

Currently, they all reside in pandas/src,
and this commit expands the lint to check
all of the following:

1) datetime (dir)
2) ujson (dir)
3) period_helper.c
4) All header files

The parser directory was handled in pandas-devgh-14740,
and the others have been deliberately omitted.

Author: gfyoung

ci/lint.sh

@@ -38,13 +38,22 @@ if [ "$LINT" ]; then
     # readability/casting: Warnings about C casting instead of C++ casting
     # runtime/int: Warnings about using C number types instead of C++ ones
     # build/include_subdir: Warnings about prefacing included header files with directory
+
+    # We don't lint all C files because we don't want to lint any that are built
+    # from Cython files nor do we want to lint C files that we didn't modify for
+    # this particular codebase (e.g. src/headers, src/klib, src/msgpack). However,
+    # we can lint all header files since they aren't "generated" like C files are.
     pip install cpplint
 
     echo "Linting *.c and *.h"
-    cpplint --extensions=c,h --headers=h --filter=-readability/casting,-runtime/int,-build/include_subdir --recursive pandas/src/parser
-    if [ $? -ne "0" ]; then
-        RET=1
-    fi
+    for path in '*.h' 'period_helper.c' 'datetime' 'parser' 'ujson'
+    do
+        echo "linting -> pandas/src/$path"
+        cpplint --extensions=c,h --headers=h --filter=-readability/casting,-runtime/int,-build/include_subdir --recursive pandas/src/$path
+        if [ $? -ne "0" ]; then
+            RET=1
+        fi
+    done
     echo "Linting *.c and *.h DONE"
 
     echo "Check for invalid testing"