clarify if MOCKABLE_FUNCTION needs a trailing semicolon or not

Hello,

I have trouble compiling some code using umock-c. The error I get is:

```
../provisioning_client/samples/custom_hsm_example/../../deps/utpm/inc/azure_utpm_c/Marshal_fp.h:16:91: error: ISO C does not allow extra ‘;’ outside of a function [-Werror=pedantic]
16 | MOCKABLE_FUNCTION(, TPM_RC, UINT8_Unmarshal, UINT8*, target, BYTE**, buffer, INT32*, size);
```

I read the documentation of umock-c and it isn't clear if MOCKABLE_FUNCTION needs that semicolon or not. The documentation uses both in examples, the requirement says calling the macro (without semicolon) should generate a function declaration with semicolon.

I can avoid this problem by removing the pedantic compiler option, so it's not really a problem for me, nonetheless, it seems a good idea to clarify the documentation about this?

Review the umock-c documentation examples and the requirement wording for MOCKABLE_FUNCTION, comparing examples that include and omit a trailing semicolon. Update the documentation so the required syntax is stated consistently and the examples follow it.

Written by the indexing model from the issue text.