custom_logo_in_customizer

custom_logo.php

// custom-logo => goes to function.php
function themeslug_theme_customizer( $wp_customize ) {
    $wp_customize->add_section( 'themeslug_logo_section' , array(
    'title'       => __( 'Branding Logo', 'themeslug' ),
    'priority'    => 30,
    'description' => 'Upload a logo to replace the default site name and description in the header',
) );
    $wp_customize->add_setting( 'themeslug_logo' );
    $wp_customize->add_control( new WP_Customize_Image_Control( $wp_customize, 'themeslug_logo', array(
    'label'    => __( 'Logo', 'themeslug' ),
    'section'  => 'themeslug_logo_section',
    'settings' => 'themeslug_logo',
) ) );
}
add_action( 'customize_register', 'themeslug_theme_customizer' );


//output in header.php (or anywhere)
<?php if ( get_theme_mod( 'enaikoon_logo' ) ) : ?>
	    <div class='site-logo'>
	        <a href='<?php echo esc_url( home_url( '/' ) ); ?>' title='<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>' rel='home'><img src='<?php echo esc_url( get_theme_mod( 'enaikoon_logo' ) ); ?>' alt='<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>'></a>
	    </div>
	<?php else : ?>
	    <hgroup>
	        <h1 class='site-title'><a href='<?php echo esc_url( home_url( '/' ) ); ?>' title='<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>' rel='home'><?php bloginfo( 'name' ); ?></a></h1>
	        <h2 class='site-description'><?php bloginfo( 'description' ); ?></h2>
	    </hgroup>
	<?php endif; ?>