Sync src with amalgamated versions

Now src contains exactly what's embedded in mongoose.c and .h, nothing more.

Added `tools/amalgam.sh` to aamlgamate both files at once.

There are no functional changes to mongoose.c, .h in this PR, only slight filename changes.

src/common/mg_str.h

@@ -0,0 +1,97 @@
+
+#ifndef CS_COMMON_MG_STR_H_
+#define CS_COMMON_MG_STR_H_
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Describes chunk of memory */
+struct mg_str {
+  const char *p; /* Memory chunk pointer */
+  size_t len;    /* Memory chunk length */
+};
+
+/*
+ * Helper function for creating mg_str struct from plain C string.
+ * `NULL` is allowed and becomes `{NULL, 0}`.
+ */
+struct mg_str mg_mk_str(const char *s);
+
+/*
+ * Like `mg_mk_str`, but takes string length explicitly.
+ */
+struct mg_str mg_mk_str_n(const char *s, size_t len);
+
+/* Macro for initializing mg_str. */
+#define MG_MK_STR(str_literal) \
+  { str_literal, sizeof(str_literal) - 1 }
+#define MG_MK_STR_N(str_literal, len) \
+  { str_literal, len }
+#define MG_NULL_STR \
+  { NULL, 0 }
+
+/*
+ * Cross-platform version of `strcmp()` where where first string is
+ * specified by `struct mg_str`.
+ */
+int mg_vcmp(const struct mg_str *str2, const char *str1);
+
+/*
+ * Cross-platform version of `strncasecmp()` where first string is
+ * specified by `struct mg_str`.
+ */
+int mg_vcasecmp(const struct mg_str *str2, const char *str1);
+
+/* Creates a copy of s (heap-allocated). */
+struct mg_str mg_strdup(const struct mg_str s);
+
+/*
+ * Creates a copy of s (heap-allocated).
+ * Resulting string is NUL-terminated (but NUL is not included in len).
+ */
+struct mg_str mg_strdup_nul(const struct mg_str s);
+
+/*
+ * Locates character in a string.
+ */
+const char *mg_strchr(const struct mg_str s, int c);
+
+/*
+ * Compare two `mg_str`s; return value is the same as `strcmp`.
+ */
+int mg_strcmp(const struct mg_str str1, const struct mg_str str2);
+
+/*
+ * Like `mg_strcmp`, but compares at most `n` characters.
+ */
+int mg_strncmp(const struct mg_str str1, const struct mg_str str2, size_t n);
+
+/*
+ * Compare two `mg_str`s ignoreing case; return value is the same as `strcmp`.
+ */
+int mg_strcasecmp(const struct mg_str str1, const struct mg_str str2);
+
+/*
+ * Free the string (assuming it was heap allocated).
+ */
+void mg_strfree(struct mg_str *s);
+
+/*
+ * Finds the first occurrence of a substring `needle` in the `haystack`.
+ */
+const char *mg_strstr(const struct mg_str haystack, const struct mg_str needle);
+
+/* Strip whitespace at the start and the end of s */
+struct mg_str mg_strstrip(struct mg_str s);
+
+/* Returns 1 if s starts with the given prefix. */
+int mg_str_starts_with(struct mg_str s, struct mg_str prefix);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* CS_COMMON_MG_STR_H_ */