The `make install` script, which most users would run via `sudo` to install into `/usr/local`, will use the current umask of the root user when creating certain files and directories. If one uses a restrictive umask by default (e.g. `umask 077`), this means that only the root user will be able to use the full Bitcoin package.

**Expected behavior**

The install script creates all directories and files, including man pages, etc., with permissions `644` / `755`.

**Actual behavior**

Certain folders are created using the default umask, e.g.:

- /usr/local/share/man/man1/
- /usr/local/lib/pkgconfig/
- [...]

This means that only root can access files in these folders and other users won't be able to read the man pages (for example).

**To reproduce**

```bash
$ ./autogen.sh
$ make
$ sudo -iu root
% umask 077
% make install
```

**System information**

OS: Linux
bitcoind version: HEAD
#include <chrono>
#include <memory>
#include <stdexcept>
#include <string>
namespace i2p {
/**
 * Swap Standard Base64 <-> I2P Base64.
 * Standard Base64 uses `+` and `/` as last two characters of its alphabet.
 * I2P Base64 uses `-` and `~` respectively.
 * So it is easy to detect in which one is the input and convert to the other.
 * @param[in] from Input to convert.
 * @return converted `from`
 */
static std::string SwapBase64(const std::string& from)
{
    std::string to;
    to.resize(from.size());
    for (size_t i = 0; i < from.size(); ++i) {
        switch (from[i]) {
        case '-':
            to[i] = '+';
            break;
        case '~':
            to[i] = '/';
            break;
        case '+':
            to[i] = '-';
            break;
        case '/':
            to[i] = '~';