curl.h: use lower case curl_mime* as for all public symbols

CURL_EXTERN int curl_strnequal(const char *s1, const char *s2, size_t n);

/* Mime/form handling support. */

typedef struct Curl_mime        curl_mime;      /* Mime context. */

typedef struct Curl_mimepart    curl_mimepart;  /* Mime part context. */

typedef struct curl_mime_s      curl_mime;      /* Mime context. */

typedef struct curl_mimepart_s  curl_mimepart;  /* Mime part context. */

/*

 * NAME curl_mime_init()

 *

 * Set mime data transfer encoder.

 */

CURL_EXTERN CURLcode curl_mime_encoder(struct Curl_mimepart *part,

CURL_EXTERN CURLcode curl_mime_encoder(curl_mimepart *part,

                                       const char *encoding);

/*