Explain the use of Go's string functions for string manipulation and processing?

Go provides a variety of built-in string functions for string manipulation and processing. Here are some examples:

**len()** - This function returns the length of a string in bytes.

str := "hello"
length := len(str) // length = 5

**strings.ToUpper()** - This function returns a new string with all characters in uppercase.

str := "hello"
newStr := strings.ToUpper(str) // newStr = "HELLO"

**strings.ToLower()** - This function returns a new string with all characters in lowercase.

str := "HELLO"
newStr := strings.ToLower(str) // newStr = "hello"

**strings.TrimSpace()** - This function returns a new string with leading and trailing white space removed.

str := "   hello   "
newStr := strings.TrimSpace(str) // newStr = "hello"

**strings.Split()** - This function splits a string into a slice of substrings based on a delimiter.

str := "hello,world"
substrings := strings.Split(str, ",") // substrings = []string{"hello", "world"}

**strings.Join()** - This function concatenates a slice of strings into a single string with a specified separator.

substrings := []string{"hello", "world"}
str := strings.Join(substrings, ",") // str = "hello,world"

**strconv.Itoa()** - This function converts an integer to a string. 

num := 42
str := strconv.Itoa(num) // str = "42"

**strconv.Atoi()** - This function converts a string to an integer.

str := "42"
num, err := strconv.Atoi(str) // num = 42, err = nil

These are just a few examples of the many string functions available in Go. By using these functions, you can easily manipulate and process string data in your programs.