Add an additional `CMakeLists.txt` file which allows building nanobind
as a standalone project, installing `libnanobind.so` under `/lib` and
headers under `/include`.

Drop the use of `typeid` and `std::type_info` from the codebase, they
are now replaced with a thin shim through `shimTypeid<T>` and
`shim::type_info`.

Search and replace all uses of uses of `std::type_info` and
`typeid(...)` from the codebase and replace them with the shimmed
functions/classes implemented in the previous commit. This commit can
be regenerated during a rebase by running the following command:

```
find src include -type f \
    \( -name '*.h' -or -name '*.cpp' \) \
    -exec sed -i \
        -e 's;std::type_info;shim::type_info;g' \
        -e 's;typeid(\*ptr);typeidShim(*ptr);g' \
        -e 's;typeid(\([^)]\+\));typeidShim<\1>();g' {} \;
```

Drop the use of exceptions from the codebase. Where needed add an
`abort`.

Search and replace all exception-related code (`try`, `catch`, `throw`)
and replace their use with functions/classes implemented in the previous
commit. This commit can be regenerated during a rebase by running the
following command:

```
find src include -type f \
    \( -name '*.h' -or -name '*.cpp' \) \
    -exec sed -i \
        -e 's|try {|if (true) {|g' \
        -e 's|catch (.*&\s*\(.\+\)) {|if (false) { shim::exception_placeholder \1;|g' \
        -e 's|catch (.*) {|if (false) {|g' \
        -e 's|throw \(.*\);$|throwShim(\1);|g' {} \;
```

Add extra compiler flags that make the compiler stricter.

Remove the `hidden` attribute from the nanobind namespace, as it was
causing linking problems.