…ze exceeds 64KB (#443)

See apache/pulsar-client-python#223

### Motivation

Currently a shared buffer is used to store serialized message metadata
for each send request. However, its capacity is only 64KB, when the metadata
size exceeds 64KB, buffer overflow could happen.

### Modifications

When the metadata size is too large, allocate a new buffer instead of
using the shared buffer. Add `testLargeProperties` to cover it.

* Expose keep alive interval for c and c++ client

* Optimize

### Motivation

When a token supplier is passed to the `AuthToken`, if exceptions are
thrown from it, the application will crash immediately. A typical case
is the Python wrapper might raise an exception when trying to get token.

### Modifications

Catch the exception in `Commands::newConnect` because the token supplier
is called in it. Then convert it to `ResultAuthenticationError`. Add
`testTokenSupplierException` to verify it.

…ed message (#462)

…cation (#467)

### Motivation

Fix some compiler warnings in public headers when using with -Wextra. These warnings prevent projects using -Wextra -Werror to use pulsar client without modifications.

### Modifications

1. Modified public headers to fix compiler warnings
2. Add compile options "-Wextra -Wno-unused-parameter" to compile examples to help find similar issues