Add CString::Contains() for convenience

This is more convenient and readable than comparing Find() to npos,
which is a common task:

$ git grep "find(" | grep "npos" | wc -l
49

include/znc/ZNCString.h

@@ -510,6 +510,13 @@ public:
 	 * @return True if the string ends with suffix, false otherwise.
 	 */
 	bool EndsWith(const CString& sSuffix, CaseSensitivity cs = CaseInsensitive) const;
+	/**
+	 * Check whether the string contains a given string.
+	 * @param s The string to search.
+	 * @param bCaseSensitive Whether the search is case sensitive.
+	 * @return True if this string contains the other string, falser otherwise.
+	 */
+	bool Contains(const CString& s, CaseSensitivity cs = CaseInsensitive) const;
 
 	/** Remove characters from the beginning of this string.
 	 * @param uLen The number of characters to remove.

src/ZNCString.cpp

@@ -1116,6 +1116,10 @@ bool CString::EndsWith(const CString& sSuffix, CaseSensitivity cs) const {
 	return Right(sSuffix.length()).Equals(sSuffix, cs);
 }
 
+bool CString::Contains(const CString& s, CaseSensitivity cs) const {
+	return Find(s, cs) != npos;
+}
+
 
 CString CString::TrimPrefix_n(const CString& sPrefix) const {
 	CString sRet = *this;

test/StringTest.cpp

@@ -198,3 +198,17 @@ TEST(StringTest, EndsWith) {
 	EXPECT_TRUE(CString("Hello, I'm Bob").EndsWith("bob", CString::CaseInsensitive));
 	EXPECT_FALSE(CString("Hello, I'm Bob").EndsWith("bob", CString::CaseSensitive));
 }
+
+TEST(StringTest, Contains) {
+	EXPECT_TRUE(CString("Hello, I'm Bob").Contains("Hello"));
+	EXPECT_TRUE(CString("Hello, I'm Bob").Contains("Hello", CString::CaseInsensitive));
+	EXPECT_TRUE(CString("Hello, I'm Bob").Contains("Hello", CString::CaseSensitive));
+
+	EXPECT_TRUE(CString("Hello, I'm Bob").Contains("i'm"));
+	EXPECT_TRUE(CString("Hello, I'm Bob").Contains("i'm", CString::CaseInsensitive));
+	EXPECT_FALSE(CString("Hello, I'm Bob").Contains("i'm", CString::CaseSensitive));
+
+	EXPECT_TRUE(CString("Hello, I'm Bob").Contains("i'm bob"));
+	EXPECT_TRUE(CString("Hello, I'm Bob").Contains("i'm bob", CString::CaseInsensitive));
+	EXPECT_FALSE(CString("Hello, I'm Bob").Contains("i'm bob", CString::CaseSensitive));
+}