Refactor decoder input stream

- Add a new field position to the json_error_t structure. This is the
  position in bytes from the beginning of the input.

- Keep track of line, column and input position in the stream level.
  Previously, only line was tracked, and it was in the lexer level, so
  this info was not available for UTF-8 decoding errors.

- While at it, refactor tests so that no separate "stripped" tests are
  required. json_process is now able to strip whitespace from its
  input, and the "valid" and "invalid" test suites now use this to
  test both non-stripped and stripped input.

Closes GH-9.

test/bin/json_process.c

@@ -7,6 +7,8 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
 #include <jansson.h>
 
 static int getenv_int(const char *name)
@@ -25,6 +27,26 @@ static int getenv_int(const char *name)
     return (int)result;
 }
 
+/* Return a pointer to the first non-whitespace character of str.
+   Modifies str so that all trailing whitespace characters are
+   replaced by '\0'. */
+static const char *strip(char *str)
+{
+    size_t length;
+    char *result = str;
+    while(*result && isspace(*result))
+        result++;
+
+    length = strlen(result);
+    if(length == 0)
+        return result;
+
+    while(isspace(result[length - 1]))
+        result[--length] = '\0';
+
+    return result;
+}
+
 int main(int argc, char *argv[])
 {
     int indent = 0;
@@ -59,9 +81,39 @@ int main(int argc, char *argv[])
     if(getenv_int("JSON_SORT_KEYS"))
         flags |= JSON_SORT_KEYS;
 
-    json = json_loadf(stdin, 0, &error);
+    if(getenv_int("STRIP")) {
+        /* Load to memory, strip leading and trailing whitespace */
+        size_t size = 0, used = 0;
+        char *buffer = NULL;
+
+        while(1) {
+            int count;
+
+            size = (size == 0 ? 128 : size * 2);
+            buffer = realloc(buffer, size);
+            if(!buffer) {
+                fprintf(stderr, "Unable to allocate %d bytes\n", (int)size);
+                return 1;
+            }
+
+            count = fread(buffer + used, 1, size - used, stdin);
+            if(count < size - used) {
+                buffer[used + count] = '\0';
+                break;
+            }
+            used += count;
+        }
+
+        json = json_loads(strip(buffer), 0, &error);
+        free(buffer);
+    }
+    else
+        json = json_loadf(stdin, 0, &error);
+
     if(!json) {
-        fprintf(stderr, "%d\n%s\n", error.line, error.text);
+        fprintf(stderr, "%d %d %d\n%s\n",
+                error.line, error.column, error.position,
+                error.text);
         return 1;
     }